Luận án tiến sĩ: Photochemistry studies of carbonylnitrenes

2.4 Photochemical Studies of Benzoyliminodibenzothiophene 32.4.1 Photoproduct Analysis of Benzoyliminodibenzothiophene 3 2.4.2 Time-Resolved Infrared Studies of Benzoyliminodibenzothioph

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Photochemistry Studies of Carbonylnitrenes

by Yonglin Liu

A dissertation submitted to Johns Hopkins University in conformity with the

requirements for the degree of Doctor of Philosophy

Baltimore, Maryland October 2006

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Although carbonylnitrenes have been well studied by product analysis, very few direct spectroscopic observations of these reactive intermediates have been made This thesis focuses on the direct observation and photochemical reactivity of carbonylnitrenes Aroyl azides are studied as photochemical precursors to aroylnitrenes Due to instability and low UV-Vis absorption of alkylcarbonyl azides, alternative photochemical precursors

to alkylcarbonylnitrenes have been developed The chemistry of carbonylnitrenes has been studied both by product analysis performed with and without trapping reagents

(alkene, oxygen, and H-atom donors) and by nanosecond time-resolved infraredspectroscopy In addition, we have also investigated the photochemical reactivity ofthiocarbonylnitrene, the sulfur analogues of carbonylnitrene Computational studies

regarding the chemistry and spectroscopy of carbonylnitrenes are also discussed

Advisor: Professor John P Toscano

Readers: Professor Gerald J Meyer

Professor Thomas Lectka

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I would like to thank many people that have assisted me for the past five years at

Johns Hopkins University First I would like to acknowledge Professor John P Toscano for time, energy, and support I would like to thank Dr Yuhong Wang for teaching me time-resolved infrared technique, Dr Walter A.Wasylenko for showing me around the office, and Dr Hua Xu for suggestions in organic synthesis I would also like to thank all the current and previous Toscano group members I would like to acknowledge our collaborators Professor Thomas Bally at University of Fribourg, Switzerland on the benzoyl azide system, Dr Nina P Gritsan at Siberian Branch of Russian Academy of

Sciences and Novosibirsk State University, Russia on the computational studies ofcarbonylnitrenes, and Professor William S Jenks at Iowa State University on

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Table of Contents

Abstract ii

Acknowledgements ili Table of Contents iv

List of Figures viil

List of Schemes XVIIList of Tables XX

Chapter 1 Introduction 1 1.1 Carbonylnitrenes 1

1.2 Alkyl- and Arylcarbonylnitrenes, Alkyl- and Aryloxycarbonylnitrenes, and 3

Thiocarbonylnitrenes

1.2.1 Alkyl- and Arylcarbonylnitrenes 3

1.2.2 Alkyl- and Aryloxycarbonylnitrenes 8

1.2.3 Alkyl- and Arylthiocarbonylnitrenes 11

1.2.4 The Curtius, Hofmann, and Lossen Rearrangements 13

1.3 | Computational Studies of Carbonylnitrenes 15

1.4 Spectroscopic Detection of Carbonylnitrenes 18

1.5 Photochemical Precursors to Carbonylnitrenes 20

1.6 References , 26Chapter 2 Photochemical Studies of Benzoylnitrene 302.1 Introduction 302.2 Time-Resolved Infrared Studies of Benzoyl Azide 322.3 Time-Resolved Infrared Studies of Diphenylsulfilimine 2 4

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2.4 Photochemical Studies of Benzoyliminodibenzothiophene 3

2.4.1 Photoproduct Analysis of Benzoyliminodibenzothiophene 3

2.4.2 Time-Resolved Infrared Studies of Benzoyliminodibenzothiophene 3

2.4.3 Proposed Photochemical Mechanism

2.5 Triplet Sensitized Photolysis of Benzoyl Azide

2.6 Photochemical Studies of Thioxanthone-based Precursor 4

2.61 Photolysis of Thioxanthone-based Precursor 4 with 266 nm Laser

3.2 Time-Resolved Infrared Studies of 4-Acetylbenzoyl Azide

3.2.1 Photolysis of Azide 1 with 266 nm Laser Excitation

3.2.2 Triplet Sensitization of Azide I with 355 nm Laser Excitation

3.2.3 Photochemical Mechanism and Discussions

3.3 Experimental

3.4 References

3.5 Supporting Information

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Chapter 4: Photochemical Studies of Thiobenzoylnitrene 136 4.1 Introduction 136 4.2 Time-Resolved Infrared Studies of Thiatriazole 137

4.3 Conclusions 147 4.4 Experimental 148 4.5 References 149 4.6 Supporting Information 152 Chapter 5: Photochemical Studies of Oxycarbonylnitrenes 169 5.1 Introduction 169 5.2 Computational Studies 171 5.3 Time-Resolved Infrared Studies of Oxycarbonyliminodibenzothiophene 1 173 5.4 Photochemical Studies of Dibenzothiophene-based Precursor 2 179

5.4.1 Product Analysis Following Photolysis of 2 179

5.4.2 Time-Resolved Infrared Studies of Dibenzothiophene-based 180

Precursor 2

5.5 Conclusions 1885.6 Experimental 1885.7 References 1905.8 Supporting Information 193Chapter 6: Photochemical Studies of Acetylnitrene and Formylnitrene 206

6.1 Introduction 206

6.2 Photochemical Studies of Acetylnitrenes | 209

6.2.1 Time-Resolved Studies of 5,5-Dihydro-5-acetyliminodibenzothiophene 209

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6.2.2 Time-Resolved Infrared Studies of 5,5-Dihydro-5- 213 trifluoroacetyliminodibenzothiophene

6.2.3 Time-Resolved Infrared Studies of 5,5-Dihydro-5- " 220

trichloroacetyliminodibenzothiophene

6 2.4 Conclusions 224

6.3 Photochemical Studies of Formylnitrene 226 6.3.1 Product Analysis After Photolysis of 6 226 6.3.2 Time-Resolved Infrared Studies of Diphenylsulfilimine 10 228

6.3.3 Time-Resolved Infrared Studies of Dibenzothiophene-based 231Precursor 6

6.3.4 Conclusions 2336.4 Experimental 2346.5 References 2366.6 Supporting Information 238

Chapter 7: Attempt to Synthesize Nitroxyl (HNO/NO) Photo-releasing 268Precursors |

7.1 Introduction 2687.2 Preliminary Results 270

7.3 Experimental ˆ 271

7.4 References 272

Curriculum Vita 275

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List of Figures

Figure 1-1 Acylnitrene 5

Figure 1-2 Aroyl azides 17 and 18.

Figure 1-3 Azide ester 30.

Figure 1-4, Resonance structures of thiocarbonylnitrenes.

Figure 1-5 Bond lengths (A) and bond angles in the singlet A’ (left) and the

triplet A” states (right) of formylnitrenes (CCSD(T)/cc-PVTZ and

B3LYP/6-31G*)

Figure 1-6 Resonance structures of alkyl- and arylcarbonylnitrenes

Figure 1-7 Acetylnitrene 49, methoxycarbonylnitrene 20, and

acetylcarbene 50

Figure 1-8 Resonance structures of alkyloxycarbonylnitrenes

Figure 1-9 Benzoyl azides

Figure 1-10 Carbonylnitrenes studied in this thesis

Figure 2-1 TRIR difference spectra observed following 266 nm laser

photolysis of benzoyl azide 1 (3.3 mM) in argon-purged acetonitrile-d,

Figure 2-2 Kinetic traces observed at (a) 1760 cm’, (b) 1635 cm" from -0.4 to

3.6 us, (c) 1635 cm” from -10 to 90 us, (d) 1570 cm”, and (e) 1520 cm’

following 266 nm laser photolysis of azide 1 (3.3 mM) in argon-purged

acetonitrile-d,

Figure 2-3 Kinetic traces observed at (a) 1760, (b) 1635, and (c) 1320 cm’

following 266 nm laser photolysis of azide 1 (3.3 mM) in argon- or

oxygen-purged acetonitrile-d,

Figure 2-4 Kinetic traces observed at (a) 1760, (b) 1680, and (c) 2265 cm”

cyclohexane

dichloromethane

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photolysis of diphenylsulfilimine 2 (1 mM) in argon-purged acetonitrile-d;.

Figure 2-7 Kinetic traces observed at (a) 1760 cm”, (b) 1635 cm” from -0.2 to

1.8 us, and (c) 1635 cm" from -10 to 90 us following 266 nm laser photolysis

of sulfilimine 2 in argon-purged acetonitrile-d,.

Figure 2-8 Kinetic traces observed at (a) 1760 and (b) 2265 cm’ following 266

nm laser photolysis of sulfilimine 2 (1 mM) in argon-purged dichloromethane.

Figure 2-9 TRIR difference spectra averaged (a) over 3.6 us and (b) over 90 us

following 266 nm laser photolysis of benzoyliminodibenzothiophene 3 (1 mM)

in argon-saturated acetonitrile-d,.

Figure 2-10 Kinetic traces observed at (a) 1758 em", (b) 1635 cm” from -0.4

to 3.6 us, (c) 1635 em” from -10 to 90 us, (d) 1485 em” from -10 to 90 us, and

(e) 1485 cm” from -0.4 to 3.6 us following 266 nm laser photolysis of

benzoyliminodibenzothiophene 3 (1 mM) in argon-saturated acetonitrile-d, and

at (f) 1758 cm" in oxygen-saturated acetonitrile-đ;.

Figure 2-11 TRIR difference spectra over (a) 1800-1460 em” and (b)

1530-1460 cm" following 266 nm laser photolysis of benzoyliminodibenzothiophene

3 (1 mM) in argon-saturated dichloromethane

following 266 nm laser photolysis of benzoyliminodibenzothiophene 3 (1 mM)

in argon-saturated dichloromethane and at (d) 1760 cm" in oxygen-saturated

dichloromethane

Figure 2-13 The trapping reactions of nitrenes with methanol observed at (a)

1760 and (b) 1485 cm following 266 nm laser photolysis of

benzoyliminodibenzothiophene 3 (1 mM) in acetonitrile-d;.

Figure 2-14 TRIR difference spectra averaged over the timescales indicated

following 355 nm laser photolysis of (a) xanthone (X, 5 mM) and (b) benzoyl

azide (1, 20 mM) in the presence of xanthone (5 mM) in argon-saturated

acetonitrile-d,

Figure 2-15 Kinetic traces observed at (a) 1635 cm” from -0.4 to 3.6 us, (b)

1635 cm’ from -10 to 90 us, (c) 1660 cm", and (d) 1480 cmTM following triplet

sensitized photolysis (355 nm) of benzoyl azide (1) (20 mM, A;,, = 0) using

xanthone (5 mM, A,s5 = 0.3) as a triplet sensitizer in argon-saturated

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following triplet sensitized photolysis (355 nm) of azide 1 (5 mM, A355 = 0)

using xanthone (5 mM, Ags; = 0.3) as a triplet sensitizer in argon-saturated

dichloromethane

Figure 2-17 10,10-Dihydro—10-benzoylimino-9H-thioxanthen-9-one (4).

photolysis of 4 (1 mM) in argon-purged acetonitrile-d,.

Figure 2-19 Kinetic traces observed at (a) 1760 em”, (b) 1520 cm”, (c) 1635

cm’ from 0.4 to 3.6 us, (d) 1320 cm” from 0.4 to 3.6 us, (e) 1635 cm” from

-10 to 90 us, and (f) 1320 cm” from 10 to 90 us following 266 nm laser

photolysis of 4 (1 mM) in argon-saturated acetonitrile-d,.

Figure 2-20 Kinetic traces observed at 1520 cm” following 266 nm laser

photolysis of 4(1 mM) in (a) argon-saturated and (b) oxygen-saturated

acetonitrile-d;

following 266 nm laser photolysis of 4 (1 mM) in argon-saturated

dichloromethane

photolysis of 4 (0.1 mM) in argon-purged acetonitrile-d,

Figure 2-23 Kinetic traces observed at (a) 1760 cm”, (b) 1720 cm”, (c) 1635

cm” from -0.4 to 3.6 us, (đ) 1520 cm", and (e) 1635 cm” from -10 to 90 us

following 355 nm laser photolysis of 4 (0.1 mM) in argon-saturated

acetonitrile-dy

photolysis of thioxanthone T (0.5 mM) in argon-purged acetonitrile-d,

Figure 2-25 Kinetic traces observed at (a) 1640 and (b) 1520 cm” following

355 nm laser photolysis of thioxanthone (0.5 mM) in argon-saturated

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photolysis of benzoyl azide 1 (3.3 mM) in argon-purged cyclohexane.

photolysis of benzoyl azide 1 (3.3 mM) in argon-purged dichloromethane.

photolysis of benzoyl azide 1 (3.3 mM) in argon-purged Freon-113.

Figure 2-29 Kinetic traces observed at (a) 1616, (b) 1660, (c) 1504, and (d)

2265 cm” following 355 nm laser photolysis of xanthone (5 mM) in

argon-saturated acetonitrile-d,

Figure 3-1 4-Acetylbenzoyl azide (1)

Figure 3-2 TRIR difference spectra averaged over the timescales following

266 nm laser photolysis of 4-acetylbenzoyl azide (1) (0.5 mM) in

Figure 3-3 Kinetic traces observed at (a) 1770 cm”, (b) 1692 cm", (c) 1640

cm” from -0.4 to 3.6 us, (d) 1560 cm”, (e) 1640 cm” from -10 to 90 us, and (f)

1286 cm" following 266 nm laser photolysis of azide 1 (0.5 mM) in

Figure 3-4 Kinetic traces observed at (a) 1760, (b) 1690, (c) 1670, (d) 1565,

(e) 1610, and (f) 2265 cm” following 266 nm laser photolysis of azide 1 (0.5

mM) in argon-saturated cyclohexane

Figure 3-5 Kinetic traces observed at (a) 1760, (b) 1665, (c) 1620, (d) 1560,

(e) 2265, and (f) 1690 cm” following 266 nm laser photolysis of azide 1 (0.5

mM) in argon-saturated dichloromethane

following 355 nm laser photolysis of (a) xanthone (X, 5 mM) and (b) azide 1 (5

mM, A355 = 0) using xanthone (5 mM, A355 = 0.3) as a triplet sensitizer in

argon-saturated dichloromethane

1690 cm” following triplet sensitized photolysis (355 nm) of azide 1 (5 mM,

Ag3ss = 0) using xanthone (5 mM, A355 = 0.3) as a triplet sensitizer in

argon-saturated dichloromethane

following triplet sensitized photolysis (355 nm) of azide 1 (5 mM, A¿s; = 0)

using xanthone (5 mM, A;;5 = 0.3) as a triplet sensitizer in argon-saturated

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dichloromethane, overlaid with bars representing B3LY P/6-31G* calculated IR

frequencies (scaled by 0.96)” and relative intensities of ylide 10.

Figure 3-9 Kinetic traces observed at (a) 1750, (b) 1665, (c) 1570, and 1720

cm” following triplet sensitized photolysis (355 nm) of azide 1 (5 mM, Ag3s5 = 0)

using xanthone (5 mM, Ass; = 0.3) as a triplet sensitizer in argon-saturated

dichloromethane

photolysis of 4-acetylbenzoyl azide (1) (0.5 mM) in argon-purged cyclohexane

Figure 3-12 Kinetic trace at 2130 cm’ following 266 nm laser photolysis of

4-acetylbenzoyl azide (1) (0.5 mM) in argon-purged cyclohexane

photolysis of 4-acetylbenzoyl azide (1) (0.5 mM) in argon-purged

dichloromethane

Figure 3-14 Kinetic traces observed at (a) 1560, (b) 1760, and (c) 1690 cm

following 266 nm laser photolysis of 4-acetylbenzoyl azide (1) (0.5 mM) in

argon- or oxygen-saturated dichloromethane

photolysis of 4-acetylbenzoyl azide (1) (0.5 mM) in argon-purged

dichloromethane

2265 cm” following 355 nm laser photolysis of xanthone (X, 5 mM) in

Figure 4-1 Singlet thiobenzoylnitrene

following 266 nm laser photolysis of thiatriazole 1 (2 mM) in argon-saturated

acetonitrile-d,

266 nm laser photolysis of thiatriazole 1 (2 mM) in argon-saturated acetonitrile

Figure 4-4 Kinetic traces observed at (a) 2230, (b) 1744, and (c) 2100 cm

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Figure 4-5 Bond lengths (A) and bond angles in the singlet and triplet states of

thiobenzoylnitrene, calculated by B3LY P/6-31G*.

Figure 4-6 The resonance of triplet benzoylnitrene *2 and biradical BR.

266 nm laser photolysis of thiatriazole 1 (2 mM) in the presence of DMSO (0.8

M) in argon-saturated acetonitrile

Figure 4-8 Bond lengths (A) and bond angles in the cyclic thiazirine 8

calculated by B3LYP/6-31G* (normal font) and MP2 calculations (italics)

266 nm laser photolysis of thiatriazole 1 (2 mM) in argon-saturated

acetonitrile-d;

acetonitrile-đ; in the presence of added DMSO (2 M)

Figure 4-11 Plot of the observed rate constant of nitrene '2 (monitored at 1740

cm”) versus the concentration of DMSO after 266 nm laser photolysis of

thiatriazole 1 in acetonitrile at ambient temperature (R’ = 0.99).

Figure 5-1 Oxycarbonyliminodibenzothiophenes and related

oxycarbonylnitrenes

Figure 5-2 Methoxycarbonylnitrene 8 and acetylnitrene 9

Figure 5-3 Resonance structures of alkyloxycarbonylnitrenes

Figure 5-4, Bond lengths (A) and bond angles in the singlet and triplet states of

t-butyloxycarbonylnitrene, calculated by B3LYP/6-31G*,

266 nm laser photolysis of 1 (3 mM) in argon-saturated acetonitrile

Figure 5-6 Kinetic traces observed at (a) 1690 cm” from -1 to 9 us, (b) 1690

cm” from -100 to 900 us, (c) 1640 cm”, and (d) 1285 cm" following 266 nm

laser photolysis of 1 (3 mM) in argon-saturated acetonitrile

Figure 5-7 Kinetic traces observed at (a) 1728, (b) 1640, and (c) 2180 cm"

following 266 nm laser photolysis of 1 (3 mM) in argon-saturated cyclohexane

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dichloromethane

266 nm laser photolysis of 2 (3 mM) in argon-saturated Freon-113

following 266 nm laser photolysis of 2 (3 mM) in argon-saturated Freon-113

following 266 nm laser photolysis of 2 (3 mM) in argon-saturated acetonitrile

Figure 5-13 Kinetic traces observed at 1640 cm" following 266 nm laser

photolysis of of 1 (3 mM) in argon-saturated acetonitrile (a) without or (b) with

triethylsilane (TES) in presence

Figure 5-14 TRIR difference spectra averaged over the timescales

indicated following 266 nm laser photolysis of 1 (3 mM) in

argon-saturated cyclohexane

following 266 nm laser photolysis of 2 (3 mM) in argon-saturated acetonitrile

Figure 5-16 'H NMR spectroscopy of

t-butyloxycarbonyliminodibenzothiophene 2 in chloroform-d

Figure 5-16 'H NMR spectroscopy of

/-butyloxycarbonyliminodibenzothiophene 2 in chloroform-d after photolysis

Figure 6-1 Resonance structures of carbonylnitrenes

Figure 6-2 Carbonyliminodibenzothiophenes and related carbonylnitrenes

Figure 6-3 N-Formyl-S,S-diphenylsulfilimine 10

photolysis of 3 (1.0 mM) in argon-purged dichloromethane

Figure 6-5 Kinetic traces observed at (a) 2255, (b) 1768, and (c) 1680 em!

following 266 nm laser photolysis of 3 (1.0 mM) in argon-purged

dichloromethane

Figure 6-6 Kinetic traces observed at (a) 1648 cm” from -0.4 to 3.6 us, (b)

1648 cm” from —100 to 900 us, and (c) 1768 cm" following 266 nm laser

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photolysis of 3 (1.0 mM) in argon-purged acetonitrile-d,.

photolysis of 4 (1.0 mM) in argon-purged dichloromethane.

following 266 nm laser photolysis of 4 (1.0 mM) in argon-purged

dichloromethane

Figure 6-10 Kinetic traces observed at (a) 1688 cm" from —-0.4 to 3.6 us, (b)

1218 cm" from -0.4 to 3.6 us, (c) 1688 em” from —100 to 900 us, (d) 1218 cm”

from —100 to 900 us, and (e) 2270 cm” following 266 nm laser photolysis of 4

(1.0 mM) in argon-purged acetonitrile.

Figure 6-11 Kinetic traces observed at (a) 1660, (b) 1688, (c) 1715, and 1218

em” following 266 nm laser photolysis of 4 (1.0 mM) in argon-purged

dichloromethane in the presence of added acetonitrile (1.0 mM).

Figure 6-13 Kinetic traces observed at (a) 1655, (b) 1720, (c) 2255, and (c)

1440 cm” following 266 nm laser photolysis of 5 (1.0 mM) in argon-purged

dichloromethane

Figure 6-14, TRIR difference spectra observed following 266 nm laser

photolysis of 5 (1.0 mM) in argon-purged acetonitrile-d,.

Figure 6-15 Kinetic traces observed at (a) 1320 cm’ from -0.4 to 3.6 us, (b)

1320 cm" from —20 to 180 us, (c) 1720 cm” from —10 to 90 us, (d) 1720 cm”

from —100 to 900 us, and (e) 1420 cm” following 266 nm laser photolysis of 5

(1.0 mM) in argon-purged acetonitrile-d,.

photolysis of 10 (3.0 mM) in argon-purged acetonitrile.

Figure 6-17 Kinetic traces observed at (a) 1654 cm’ from -0.4 to 3.6 us, (b)

1231 cm from -0.4 to 3.6 us, (c) 1654 cm” from —100 to 900 us, (d) 1231 cm’

from —100 to 900 us, and (e) 2270 cm" following 266 nm laser photolysis of 10

(3.0 mM) in argon-purged dichloromethane.

photolysis of 6 (3.0 mM) in argon-purged acetonitrile.

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Figure 6-19 Kinetic traces observed at (a) 1654 and (b) 1231 cm’ following

266 nm laser photolysis of 6 (3.0 mM) in argon-purged dichloromethane

Figure 6-20 Kinetic traces observed at 1768 cm' following 266 nm laser

photolysis of 3 in argon-purged dichloromethane

Figure 6-22 Kinetic traces observed at 1660 and 1715 cm’ following 266 nm

laser photolysis of 4 in argon-purged dichloromethane with added methanol

(0.4 M)

Figure 6-24 'H NMR spectroscopy of formyliminodibenzothiophene 6 in

DMSO-d, before photolysis

DMSO-d, after photolysis

acetonitrile-d, before photolysis

acetonitrile-d, after photolysis

Figure 7-1 Nitroxyl donors

Figure 7-2 Dibenzothiophene-based HON precursor

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Typical one-step reaction of singlet nitrenes.

Typical two-step reaction of triplet nitrenes.

Trapping of singlet and triplet nitrenes with cis-2-butene

The Lossen rearrangement |

The photo-Curtius rearrangement

Photoproduct analysis of acyl azide 1

Photochemical studies of benzoyl azide 6

Photosensitization studies of benzoyl] azide 6

Photolysis of 2-naphthoyl azide 12

Photosensitization of 2-naphthoyl azide 12

Photolysis of methoxycarbonyl azide 19

Formation of ethoxycarbonylnitrene 24 and its reaction withReactions of ethoxycarbonylnitrene 24 with alkenes

Photolysis of 7-butyloxycarbonyl azide

Photolysis of azide 23 in nitriles

Thermolysis of thiatriazole 35

Photolysis of 5-phenyl-1,2,3 ,4-thiatriazole 38

Photolysis of 5-phenyl- 1 ,2,3 ,4-thiatriazole 38

Mechanisms for the Curtius, Hofmann, and Lossen

reatrangements

Scheme 1-20 Thermal decomposition of pivaloylazide 44

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Scheme 1-21 Photolysis of pivaloylazide 44.

Scheme 1-22 Kinetic isotope effects (KIE) of carbons and nitrogens in the

Curtius, Hofmann, and Lossen Rearrangements.

Scheme 1-23 Photolysis of carboethoxy azide 23.

Scheme 1-24 Photolysis of benzoyl azide 6.

Scheme 1-25 Trimethylammonium dodecanoylimide 53 and azide 56 as

carbonylnitrene precursors

Scheme 1-26 Phenyl nitrile oxides 58 as carbonylnitrene precursors.

Scheme 1-27 Heterocyclic compounds 62 as carbonylnitrene precursors.

Scheme 1-28 Photochemical precursors to triplet oxygen

Scheme 1-29 Sulfilimines as photochemical precursors of carbonylnitrenes

Scheme 1-30 Photochemical precursors to thiobenzoylnitrene.

Scheme 2-1 Photochemical precursors to benzoylnitrene

Scheme 2-2 Photochemical reactivity of benzoyl azide 1

Scheme 2-3 Photochemical reactivity of sulfilimine 2

Scheme 2-4 Photochemical reactivity of benzoyliminodibenzothiophene 3

Scheme 2-5 Proposed photochemical mechanism

Scheme 2-6 Photolysis of xanthone

Scheme 2-7 Proposed triplet sensitization mechanism of azide 1

Scheme 2-8 Photolysis of thioxanthone

Scheme 3-1 Proposed photochemical mechanism of 4-acetylbenzoyl azide (1)

by Schuster and co-workers

Scheme 3-2 Proposed photochemical mechanism

Scheme 3-3 Photolysis of xanthone

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Reaction of singlet nitrene 12 with xanthone X.

Proposed photochemical mechanism on the basis of our TRIR

Proposed photochemical mechanism by Holm and co-workers

Our proposed photochemical mechanism of thiatriazole 1.

Resonance structures of carbonylnitrenes and thiocarbonylnitrenes

Photolysis of azide Al

Photolysis or thermolysis of azide A2

Proposed photochemical mechanism of 1

Proposed photochemical mechanism of 2

Resonance structures of carbonylnitrenes with zwitterionic

Resonance structures of singlet diphenylphosphorylnitrene

Aqueous decomposition of Angeli's salt (AS) yields nitrite and

Photochemical equilibrium of HNO and HON

The first attempt of synthesizing HON-releasing precursor

The future attempt of synthesizing HON-releasing precursor

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List of Tables

Table 1-1 Singlet-triplet energy gap [AEsr (kcal/mol)] of species 49, 20, and 50

by DFT, CCSD(T), and CBS-QB3 methods

Table 1-2 Absolute rate constants for reactions with benzoylnitrene 8 with

various quenchers at ambient temperature

Table 2-1 Yields of products following direct or triplet sensitized photolysis of

benzoyliminodibenzothiophene 3 in argon- or oxygen-purged methanol-d,

Table 2-2 Yields of products following direct and triplet sensitized photolysis of

benzoyliminodibenzothiophene 3 in argon-purged isopropanol

Table 2-3 Optimized geometry and energy for singlet benzoylnitrene ‘5.

Table 2-4 Optimized geometry and energy for triplet benzoylnitrene °5.

Table 2-5 Optimized geometry and energy for ylide 11

Table 2-6 Optimized geometry and energy for azirine 12.

Table 2-7 Optimized geometry and energy for amide 15

Table 2-8 Optimized geometry and energy for amide 16

Table 2-9 B3LYP/6-31G* calculated frequencies (cm”, unscaled) and intensities

for singlet benzoylnitrene ‘5.

Table 2-10 B3LYP/6-31G* calculated frequencies (cm, unscaled) and

intensities for triplet benzoylnitrene *5.

Table 2-11 B3LYP/6-31G* calculated frequencies (cm”, unscaled) and

intensities for ylide 11

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Table 2-12 B3LYP/6-31G* calculated frequencies (em”, unscaled) and

intensities for azirine 12.

Table 2-13 B3LYP/6-31G* calculated frequencies (cm’, unscaled) and

intensities for amide 15

Table 2-14 B3LYP/6-31G* calculated frequencies (cm', unscaled) and

intensities for amide 16

Table 2-15 Optimized geometry and energy for triplet excited state of

dibenzothiophene (DBT)

Table 2-16 B3LYP/6-31G* calculated IR frequencies (cm, unscaled) and

intensities for triplet excited state of dibenzothiophene (DBT)

Table 2-17 Optimized geometry and energy for triplet excited state of azide 1

intensities for the lowest triplet excited state of benzoyl azide 1

Table 3-1 Optimized geometry and energy for singlet 4-acetylbenzoylnitrene ‘2.

Table 3-2 Optimized geometry and energy for triplet 4-acetylbenzoylnitrene *2.

Table 3-3 Optimized geometry and energy for singlet 4-acetylbenzoylnitrene

and xanthone ylide 10

intensities for singlet 4-acetylbenzoylnitrene and xanthone ylide 10

Table 3-5 Optimized geometry and energy for triplet excited state of

4-acetylbenzoyl azide (71*).

Table 3-6 B3LYP/6-31G* calculated frequencies (cm”, unscaled) and intensities

for triplet excited state of 4-acetylbenzoyl azide *1*.

Table 4-1 Thiobenzoylnitrene singlet '2 B3LYP/6-31G* optimized geometry

(coordinates in A) and energy.

Table 4-2 Thiobenzoylnitrene triplet 32 B3LYP/6-31G* optimized geometry

(coordinates in A) and energy —

123124

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Table 4-3 Benzonitrile sulfide 4 B3LY P/6-31G* optimized geometry

Table 4-4 Sulfoximine 7 B3LYP/6-31G* optimized geometry (coordinates in A)

and energy

Table 4-5 B3LYP/6-31G* calculated frequencies (cm", unscaled) and

intensities for singlet thiobenzoylnitrene ‘2.

intensities for triplet thiobenzoylnitrene `2.

intensities for benzonitrile sulfide 4.

intensities for sulfoximine 7

Table 4-9 B3LYP/6-31G* calculated charges and spins for triplet

Table 5-2 The formation ratios of oxazolidinone 5 following a biexponential fit

in term of dielectric constants of different solvents

Table 5-3 t-Butyloxycarbonylnitrene singlet '4 B3LY P/6-31G* optimized

geometry (coordinates in A) and energy.

Table 5-4 t-Butyloxycarbonylnitrene triplet °4 B3LYP/6-31G* optimized

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Table 5-5 Ethoxycarbonylnitrene singlet 13 B3LYP/6-31G* optimized geometry

Table 5-6 Ethoxycarbonylnitrene triplet °3 B3LY P/6-31G* optimized geometry

intensities for singlet /-butyloxycarbonylnitrene '4.

Table 5-8 B3LYP/6-31G* calculated IR frequencies (cm”, unscaled) and:

intensities for triplet t-butyloxycarbonylnitrene 34.

Table 5-9 B3LYP/6-31G* calculated IR frequencies (cm”, unscaled) and

intensities for singlet ethoxycarbonylnitrene '3.

Table 5-10 B3LYP/6-31G* calculated IR frequencies (cm', unscaled) and

intensities for triplet ethoxycarbonylnitrene 33.

Table 6-1 Yields of products following photolysis of 6 in acetonitrile-d, or

dimethyl sulfoxide-d, solutions.

Table 6-2 Acetylnitrene singlet '1 B3LYP/6-31G* optimized geometry

Table 6-3 Acetylnitrene triplet *1 B3LYP/6-31G* optimized geometry

Table 6-4 Trifluoroacetylnitrene singlet '4 B3LYP/6-31G* optimized geometry

Table 6-5 Trifluoroacetylnitrene triplet °4 B3LYP/6-31G* optimized geometry

Table 6-6 Trichloroacetylnitrene singlet +5 B3LYP/6-31G* optimized geometry

Table 6-7 Trichloroacetylnitrene triplet *5 B3LYP/6-31G* optimized geometry

Table 6-8 Formylnitrene singlet ‘9 B3LYP/6-31G* optimized geometry

Table 6-9 Formylnitrene triplet °9 B3LY P/6-31G* optimized geometry

Trang 25

Table 6-10 Trifluoroacetylnitrene-acetonitrile ylide B3LYP/6-31G* optimized

Table 6-11 Acetylnitrene-acetonitrile ylide B3LYP/6-31G* optimized

Table 6-12 Trichloroacetylnitrene-acetonitrile ylide B3LYP/6-31G* optimized

Table 6-13 B3LYP/6-31G* calculated IR frequencies (cm", unscaled) and

intensities for singlet acetylnitrene ‘1.

intensities for triplet acetylnitrene *1.

Table 6-15 B3LYP/6-31G* calculated IR frequencies (cem”, unscaled) and

intensities for singlet trifluoroacetylnitrene '4.

intensities for triplet trifluoroacetylnitrene 34.

Table 6-17 B3LYP/6-31G* calculated IR frequencies (cm”’, unscaled) and

intensities for singlet trichloroacetylnitrene ‘5.

Table 6-18 B3LYP/6-31G* calculated IR frequencies (cem”, unscaled) and |

intensities for acetylnitrene-acetonitrile ylide

intensities for singlet formylnitrene '9.

intensities for triplet formylnitrene °9.

Table 6-21 B3LYP/6-31G* calculated IR frequencies (cm’, unscaled) and

intensities for triftuoroacetylnitrene-acetonitrile ylide

intensities for trichloroacetylnitrene-acetonitrile ylide

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Chapter 1: Introduction

1.1 Carbonylnitrenes

Nitrenes are compounds containing a neutral monovalent nitrogen atom.'? Similar

to carbenes, nitrenes are usually short-lived reactive intermediates Imidogen (NH),” alkylnitrenes (RN), and arylnitrenes (ArN)” have been well studied Recently, the Toscano group has investigated the chemistry and spectroscopy of oxynitrenes” and sulfenylnitrenes.° This thesis mainly concerns the similar study of carbonylnitrenes.Although carbonylnitrenes have been well studied by product analysis, only a few directspectroscopic observations have been made.””!

Carbonylnitrenes have two important electronic configurations, singlet and triplet.The singlet nitrene SN has two pairs of electrons occupying two orbitals of the nitrogenatom; one orbital remains empty Therefore, SN is electrophilic, and it can react with anunshared electron pair on a heteroatom, with a x system, or even with electrons in a C-Hbond in a concerted process (Scheme 1-1) The triplet nitrene TN, on the other hand, hastwo single electrons in two orbitals of the nitrogen atom TN is more like a 1,1-diradical

and it usually reacts in two steps (Scheme 1-2)

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The reaction of nitrenes with alkenes can aid in the determination of the groundspin state of nitrenes.

afford more than one isomer of the aziridine product If the ground state of the nitrene is

a singlet, then the reaction occurs concerted and stereospecifically; if the ground state is atriplet, then a stepwise reaction occurs and a mixture of isomers are obtained (Scheme 1-3)

concerted _

O

_Stepwise _ (= ^ | ——~ Ñ _Totate _ aks ` : A ,

Scheme 1-3 Trapping of singlet and triplet nitrenes with cis-2-butene

Scheme 1-1 Typical one-step reaction of singlet nitrenes

Scheme 1-2 Typical two-step reaction of triplet nitrenes

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12,13 14,15

Imidogen, alkylnitrenes, and oxynitrenes® have all been found to have

triplet ground states Likewise, carbonylnitrenes were originally believed to have triplet

ground states However, recent studies''”° have found that significant orbital overlap

between O and N in carbonylnitrenes presumably the stabilizes singlet state and lower the

singlet and triplet energy gap (AE,,) Thus, many carbonylnitrenes have singlet ground

states

12 Alkyl- and Arylcarbonylnitrenes, Alkyl- and

Aryloxycarbonylnitrenes, and Thiocarbonylnitrenes

1.21 Alkyl- and Arylcarbonylnitrenes

Alkyl- and arylcarbonylnitrenes R-CO-N (R = alkyl or aryl) were first proposed

as reactive intermediates in the Lossen rearrangement (Scheme 1-4) by Tiemann in1891.” The reactions of alkylcarbonylnitrenes were not observed until 1965 by Edwards and co-workers.'*? Photolysis of azide 1 is found to produce 25% ô-lactam 3and a trace of y-lactam 4, along with isocyanate 2 (70%), a photo-Curtius (Scheme 1-5)

product Amides 3 and 4 apparently arise from the cyclization reactions of

carbonylnitrene 5 (Figure 1-1) by intramolecular C-H bonds insertion (Scheme 1-6)

Trang 29

4 (trace)

Scheme 1-6 Photoproduct analysis of acyl azide 1

Figure 1-1, Acylnitrene 5

Horner and co-workers detected intermolecular nitrene products after photolysis

of benzoyl azide 6 Benzoylnitrene 8 is found to be trapped with water, acetic acid, or

aniline, to produce the corresponding O-H or N-H insertion products, and with dimethyl

Trang 30

sulfoxide (DMSO) to yield sulfoximine 9 Thermolysis of 6, on the other hand, leads

exclusively to phenylisocyanate 7 (Scheme 1-7).”°”"

Ph + Phí NTR!

we H

le)DMSO

ASPh* `N=S=O

\

9

Scheme 1-7 Photochemical studies of benzoyl azide 6

Triplet sensitized photolysis of azide 6 leads to formation of benzamide 11

Triplet nitrene 10 has been proposed as an intermediate in this process (Scheme 1-8).”

Scheme 1-8 Photosensitization studies of benzoyl azide 6

Alkyl- and arylcarbonylnitrenes were originally believed to have triplet ground

states.””* This assumption, however, was questioned, since only singlet nitrenes trapping

products are observed following direct photolysis of the corresponding azides Inagaki

and co-workers” demonstrated that direct and triplet sensitized photolysis of benzoyl

Trang 31

azide 6 in cis and trans-alkene produces the same products, which are characteristic of singlet nitrenes On the basis of these results, they proposed that the singlet nitrene 8 and triplet nitrene 10 are in equilibrium, and the singlet nitrene is much more reactive than the triplet nitrene Nevertheless, the EPR spectrum of triplet benzoylnitrene 10 could not be

detected after photolysis of benzoyl azide 6 in glassy matrics.47""

Schuster and Autrey'° found that photolysis of 2-naphthoyl azide (12) in the

presence of cis-4-methyl-2-pentene yields azirine 15 stereospecifically (Scheme 1-9)

The azirine 16, a related triplet nitrene product, was not detected The observation ofonly singlet nitrene trapping products can be explained either by reaction from the singletground state of nitrene, or a very slow relaxation rate from singlet nitrene 13 to triplet

nitrene 14 The latter possibility was eliminated by a triplet sensitization experiment

With 2-propylthioxanthone as the triplet sensitizer, photosensitization of azide 12 againproduces azirine 15 exclusively (Scheme 1-10) Therefore, it is very likely that 2-

naphthoylnitrene has a singlet ground state."°

Scheme 1-9 Photolysis of 2-naphthoyl azide 12

Trang 32

Scheme 1-10 Photosensitization of 2-naphthoyl azide 12.

In later work, Schuster and co-workers investigated other similar azides, such as

aroyl azides 17 and 18.” Both of these azides have an internal sensitizing group, whichpresumably favors the formation of triplet nitrenes Following photolysis of 17 and 18,however, only singlet nitrene trapping products are observed In addition, low-

temperature photolysis of 12, 17, and 18 fails to produce EPR signals consistent with a

triplet nitrene Thus, these aroylnitrenes must all have singlet ground states

17 18

Figure 1-2 Aroyl azides 17 and 18

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1.22 Alkyl- and Aryloxycarbonylnitrenes

Alkyl- and aryloxycarbonylnitrenes are usually formed following thermolysis or photolysis of the corresponding azides For instance, methoxy isocyanate 21 is observed after following photolysis of methoxycarbonyl azide 19 in an Ne matrix at 6 K.

Methoxycarbonylnitrene 20 has been proposed as a potential intermediate (Scheme 102

1-Oo hv O

yf 1® _„ ——> N=G:OMeO” “Ng MeOZ ~N: MeO

19 20 21

Scheme 1-11 Photolysis of methoxycarbonyl azide 19.

Ethoxycarbonylnitrene 24 has been generated from based-catalyzed œ-elimination

of N-(p-nitrobenzenesulfonyloxy)-urethane 22” or photolysis of ethyl azidoformate 23.” Nitrene 24 reacts with cyclohexene to form azirine 25 and C-H bond insertion products

26 and 27 (Scheme 1-12)

39

0 base fe) o HN7SoEt

Trang 34

The reaction of ethoxycarbonylnitrene 24 with cis-4-methyl-2-pentene has also

been examined? The reactivity of !24 and °24 is dependent on the concentration of

alkene In presence of large concentrations of alkene only the singlet nitrene trapping product 28 is observed, while in diluted alkenes both singlet and triplet nitrene trapping products 28 and 29 are observed The degree of stereospecificity of nitrene products

decreases drastically with the reduction of alkene concentration This observation indicates that the singlet intermediate is formed first and then relaxes to a lower energy

triplet intermediate

HO“ “Ng EtO

Scheme 1-13 Reactions of ethoxycarbonylnitrene 24 with alkenes

In addition, photolysis of azide ester 23 and 30 at cryogenic temperatures leads to

EPR signals that are consistent with triplet nitrenes.”?” Thus, alkyl- and

aryloxycarbonylnitrenes have triplet ground states

Trang 35

Figure 1-3 Azide ester 30

Hafner and co-workers performed product analysis following photolysis of butyloxycarbonyl azide 31 in different solvents They found after photolysis of azide 31 the major product (75%) observed is 5,5-dimethyl-2-oxazolidinone 32 independent ofsolvent used (Scheme 1-14) Photolysis of carbethoxy azide 23 produce 1,3 ,4-oxadiazole

/-34 as the major product in acetonitrile Nitrene-nitrile ylide 33 has been proposed as the

Scheme 1-15 Photolysis of azide 23 in nitriles.

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1.23 Alkyl- and Arylthiocarbonylnitrenes

Sulfur analogues of carbonylnitrenes, alkyl- or arylthiocarbonylnitrenes 36, have been proposed as intermediates in the formation of isothiocyanate 37 for certain thermal processes.***? Common precursors of thiocarbonylnitrenes are heteroaromaticthiatriazoles 35

R = Alkyl or aryl

Scheme 1-16 Thermolysis of thiatriazole 35

Okazaki and co-workers” found that photodecomposition of thiatriazole 38 in presence of cyclohexene led to the formation of episulfide 40, which isformed from the reaction of triplet sulfur with olefin A mechanism has been proposedinvolving both singlet and triplet thiobenzoylnitrene 39 (Scheme 1-17)

Scheme 1-17 Photolysis of 5-phenyl-1,2,3,4-thiatriazole 38

Irradiation of 5-phenyl-1,2,3,4-thiatriazole 38 with UV light, first studied byKirmse,” affords benzonitrile (66%), sulfur (76%), and phenyl isothiocyanate 5 (7.3%).

Trang 37

Holm and co-workers^2“ found that the main route for photolytic product formation takes

place from the singlet excited state, and observed benzonitrile sulfide 42 by temperature UV spectroscopy (Scheme 1-18) Additionally, the yield of isothiocyanate

low-43 was found to be independent of the solvents employed (isopropanol, acetonitrile, and

dichloromethane) and was not affected by the presence of oxygen A triplet nitrene

signal was not detected by EPR spectroscopy after photolysis of 38 Benzonitrile sulfide

42 was proposed to be formed via thiazirine intermediate 41, but not thiobenzoylnitrene

39 As will be discussed in Section 4, thiazirine 41 and thiobenzoylnitrene 39 aredifferent representations of the same intermediate, and the minimum energy geometry of

this intermediate is between that of a thioacylnitrene and a thiazirine (Figure 1-4)

N hv

ox ——_ Ph-C=N-S ——~ PhCN + S

41 42Scheme 1-18 Photolysis of 5-phenyl-1,2,3 4-thiatriazole 38

Ss _ Sminor major

Figure 1-4 Resonance structures of thiocarbonylnitrenes

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1.24 The Curtius, Hofmann, and Lossen Rearrangements

As has been discussed in Section 1.21, carbonylnitrenes were postulated by

Tiemann” and Stieglitz as possible intermediates involved in the Curtius, Hofmann, and

Lossen rearrangements (Scheme 1-19) The most obvious alternative mechanism to the

stepwise process I is a concerted pathway II, where the leaving group departs at the sametime as the migrating group makes the new bond to nitrogen Since carbonylnitrenes can

be trapped efficiently with alcohols, alkanes, and alkenes, one can possibly test thestepwise nitrene mechanism I by simple trapping experiments

Lwowski and co-workersS“ performed a comprehensive study of the

decomposition of pivaloylazide 44 Thermal decomposition of 44 in neat cyclohexeneleads to tert-butylisocyanate 47 as the only product in nearly quantitative yield.Therefore, the thermal Curtius rearrangement (Scheme 1-20) is likely a concertedprocess Photolysis of 44 in neat cyclohexene, on the other hand, produces azirine adduct

46 Tert-butylisocyanate 47 is also produced

Trang 39

Q A

a N=C=O

44 47 ~100%

Scheme 1-20 Thermal decomposition of pivaloylazide 44.

Additional photochemical studies of 44 in different solvents such as dichloromethane, cyclohexane, or 2-methylbutane indicate that the yield of tert- butylisocyanate 47 (40%) is independent of the solvents used and that trapping reactions

of nitrene 45 do not decrease the yield of 47 On the base of these results, it was concluded that isocyanate 47 and trapping adducts 46 or 48 cannot be produced from the

same intermediate 45 Instead, isocyanate 47 was proposed to be formed from the singlet

excited state of azide !44* (Scheme 1-21).

Trang 40

The most convincing evidence for a concerted mechanism is probably the kinetic

isotopic effect (KIE) experiments of Fry and Wright.” They measured the KIE for the

migrating group, the carbonyl group, and the migration terminus of the Curtius, Hofmann, and Lossen Rearrangements (Scheme 1-22) Substantial isotope effects for the migrating carbon, the migrating nitrogen, and the leaving nitrogen (Curtius rearrangement) indicate that all three are involved in the rate-determining step Thus,

these reactions likely proceed via a concerted mechanism

0.018 0.012 o 7° 009O

i, xi ¢ ye C vớ

= =N —4 N-Br 7 OCOCaH;

LIỀN j tì

0042 0037 0.037 0.044 0.035 0.033 sả»

Curtius Rearrangement Hofmann Rearrangement Lossen Rearrangement

Scheme 1-22 Kinetic isotope effects (KIE) of carbons and nitrogens in the Curtius,Hofmann, and Lossen Rearrangements

1.3 Computational Studies of Carbonylnitrenes

Density function theory (DFT) calculations have been performed by Gritsan and

co-workers on the properties of the singlet and triplet states of benzoylnitrene,

naphthoylnitrene, and formylnitrene.'"! The geometry of the C(O)N fragment in the

lowest singlet and triplet states of nitrenes R-C(O)N and the singlet — triplet energy gap

(AEgr = Es - Ez) have been found to be relatively insensitive to the replacement of the

Tiêu đề	Photochemistry Studies of Carbonylnitrenes
Tác giả	Yonglin Liu
Người hướng dẫn	Professor John P. Toscano, Professor Gerald J. Meyer, Professor Thomas Lectka
Trường học	Johns Hopkins University
Chuyên ngành	Chemistry
Thể loại	Dissertation
Năm xuất bản	2006
Thành phố	Baltimore

Định dạng
Số trang	300
Dung lượng	22,7 MB