bài tập phổ hữu cơ IR NMR 2

Cho đến nay các phương pháp phổ học được lựa chọn là: hồng ngoại, tử ngoại, khối lượng và cộng hưởng hạt nhân. Nhiệm vụ của phổ tử ngoại là phát hiện các hệ thống tiếp cách (conjugated), bởi vì sự kích thích các điện tử từ trạng thái cơ bản lên trạng thái kích thích của những hệ thống như thế mới gây nên sự hấp thu trong vùng tử ngoại. Nhưng sự phát triển hiện nay của các kĩ thuật cộng hưởng từ hạt nhân đã đạt đến mức có thể giảm tối đa vai trò của phổ tử ngoại. Hơn nữa, nhiều dao động của nhiều liên kết hoá học không hoạt động trong phổ hồng ngoại, mà hoạt động trong phổ Raman, do đó phổ học Raman được chọn bổ sung cho việc nghiên cứu dao động của các phân tử hữu cơ

Problem 1

C5H10O

MW 86 The band at 1716 indicates a carbonyl, probably a ketone The bands at 3000-2850 indicate C-H alkane stretches

Problem 1, NMR intrepreted

Problem2

C7H14O

MW 114 The band at 1718 indicates a carbonyl, probably a ketone The bands at 3000-2850 indicate C-H alkane stretches

Prob 2 NMR, interpreted

Problem 3

C4H10O

MW 74 The broad band at 3339 indicates O-H stretch, probably an alcohol The bands at 3000-2850 indicate C-H alkane

stretches The band at 1041 is C-O stretch, consistent with an alcohol

Prob 3 NMR, interpreted

Problem 4

C6H14O

MW 102 The broad band at 3350 indicates O-H stretch, probably an alcohol The bands at 3000-2850 indicate C-H alkane

stretches The bands from 1320-1000 indicate C-O stretch, consistent with an alcohol

Prob 4 NMR, interpreted

Note that the structure has a chiral center and the mixture is racemic Methylene protons adjacent to a chiral center

may not be identical

Problem 5

C4H8O2

MW 88 Prob 5, IR answer The band at 1743 indicates a carbonyl, probably a saturated aliphatic ester The bands at 3000-2850 indicate C-H alkane stretches The bands in the region 1320-1000 could be due to C-O stretch, consistent with an ester

Prob 5 NMR, interpreted

Problem 6

C5H10O2

MW 102 Prob 6, IR answer The band at 1740 indicates a carbonyl, probably a saturated aliphatic ester The bands at 3000-2850 indicate C-H alkane stretches The bands in the region 1320-1000 could be due to C-O stretch, consistent with an ester

Prob 6 NMR, interpreted

Problem 7

C5H10O

MW 86 Prob 7, IR answer The band at 1728 indicates a carbonyl, probably an aldehyde; an aldehyde is also suggested by the band at 2719 which is likely the C-H stretch of the H-C=O group The bands at 3000-2850 indicate C-H alkane stretches

Prob 7 NMR, interpreted

Problem 8

C8H8O

MW 120 Prob 8, IR answer The band at 1703 indicates a carbonyl; that the carbonyl is an aldehyde is suggested by the bands at 2828 and

2733 (C-H stretch of the H-C=O group) The bands at 3000-2850 indicate C-H alkane stretches The band

(unmarked on the graph below) just to the left of 3000 indicates aromatic C-H stretch Aromatics also show bands

in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane)

Prob 8 NMR, interpreted

assign the individual peaks in the aromatic region to specific hydrogens on the aromatic ring The aromatic

protons show a pattern characteristic of para substitution

Problem 9

C9H10O2

MW 150 Prob 9, IR answer The band at 1697 indicates an alpha, beta-unsaturated carbonyl; that the carbonyl is an aldehyde is suggested by the bands at 2828 and 2739 (C-H stretch of the H-C=O group) The bands at 3000-2850 indicate C-H alkane stretches The band (unmarked on the graph below) just to the left of 3000 indicates aromatic C-H stretch Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-

of-plane)

Prob 9 NMR, interpreted

Problem 10

C3H6O2

MW 74 Prob 10, IR answer The band at 1716 indicates a carbonyl The wide band from 3300-2500 is characteristic of the O-H stretch of carboxylic acids The bands at 3000-2850 indicate C-H alkane stretches The bands in the region 1320-1000

indicate the C-O stretch of carboxylic acids

Prob 10 NMR, interpreted

Problem 11

C11H14O2

MW 178 Prob 11, IR answer The band at 1684 indicates a carbonyl The wide band from 3300-2500 is characteristic of the O-H stretch of carboxylic acids The bands at 3000-2850 indicate C-H alkane stretches The bands in the region 1320-1000 indicate the C-O stretch of carboxylic acids The band (unmarked on the graph below) just to the left of 3000 indicates aromatic C-H stretch Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring

stretch), and 900-675 (C-H out-of-plane)

Prob 11 NMR, interpreted

Problem 12

C8H8O2

MW 136 Prob 12, IR answer The band at 1684 indicates a carbonyl The wide band from 3300-2500 is characteristic of the O-H stretch of carboxylic acids The bands at 3000-2850 indicate C-H alkane stretches The bands in the region 1320-1000 indicate the C-O stretch of carboxylic acids The band just to the left of 3000 (3065) indicates aromatic C-H stretch Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675

(C-H out-of-plane)

Prob 12 NMR, interpreted

Problem 13

C7H9N

MW 114 Prob 13, IR answer The two bands at 3433 and 3354 indicate a secondary amine The bands at 3000-2850 indicate C-H alkane stretches The band at 3034 indicates aromatic C-H stretch; aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane) C-N stretch of aromatic amines would

show up at 1335-1250 (there is a band in that region)

Prob 13 NMR, interpreted

Problem 14

C5H13N

MW 87 Prob 14, IR answer The two bands at 3388 and 3292 indicate a secondary amine The bands at 3000-2850 indicate C-H alkane

stretches

Prob 14 NMR, interpreted

Problem 15

C8H14O

MW 126 Prob 15, IR answer The band at 1718 indicates a carbonyl, probably a ketone The bands at 3000-2850 indicate C-H alkane stretches Since the compound is an alkene, one would expect to see C=C stretch at 1680-1640; these weak bands are not

seen in this IR (according to Silverstein, "the C=C stretching mode of unconjugated alkenes usually shows

moderate to weka absorption at 1667-1640") Since the compound is an alkene, C-H stretch should appear above

3000 (not seen: the absorption for this single hydrogen must be too weak)

Prob 15 NMR, interpreted

Problem 16

C4H9Br

MW 137 Prob 16, IR answer The bands at 3000-2850 indicate C-H alkane stretches The bands in the region 1300-1150 could indicate C-H

wag (-CH2Br) of an alkyl halide

Prob 16 NMR, interpreted

Problem 17

C10H14O

MW 150 Prob 17, IR answer The bands at 3000-2850 indicate C-H alkane stretches; the small (unmarked) band just to the left of 3000

indicates aromatic C-H stretch Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane) The wide band in the region 3500-3200 indicates the O-H stretch of an

alcohol or phenol

Prob 17 NMR, interpreted

Problem 18

C13H10O3

MW 214 Prob 18, IR answer The band at 1682 indicates a carbonyl, probably an ester The band at 3192 indicates C-H aromatic stretch; aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane) The wide band just to the left of the 3192 band indicates O-H stretch (alcohols and phenols)

Prob 18 NMR, interpreted

Note: the correct placement of the -OH on the ring and the arrangement of the ester may be beyond the scope of

your spectroscopy course See this explanation

Problem 18, structure

Problem 19

C8H14

MW 110 Prob 19, IR answer The bands at 3000-2850 indicate C-H alkane stretches There really aren't many other bands in the spectrum to indicate functional groups The compound is an alkyne; we would expect to see a carbon-carbon triple bond

stretch at 2260-2100, however, this is a weak band at best and often does not show up on IR

Prob 19 NMR, interpreted

Problem 20

C9H13N

MW 135 Prob 20, IR answer The bands at 3000-2850 indicate C-H alkane stretches The band at 3028 indicates C-H aromatic stretch;

aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H of-plane) The bands in the region 1250-1020 could be due to C-N stretch The weak, broad banc at about 3500 could be amine N-H stretch or it could be a slight contamination of an impurity (water) in the sample

out-Prob 20 NMR, interpreted

Problem 21

C9H10

MW 118 Prob 21, IR answer The bands at 3000-2850 indicate C-H alkane stretches The band at 3060 indicates C-H aromatic stretch;

aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H

out-of-plane)

Prob 21 NMR, interpreted

Part I Multiple Choice (0 pts total)

1 Co sider the folowin IR spe trum (0 pts)

The inf ared spe trum su gest the presenc of

a) a c rb x l c a id an an aromat c rin b) a c rb x l c a id an a keto e c) an alco ol an an aromat c rin d) an alco ol an an alkene

2 Co sider the mole ule depicted How wo ld the gro p labeled as ‘a’ wo ld ap e r in the 1H NMR

spe trum? (0 pts

a) sin let b) d u let c) triplet d) q artet

H H

H H

Part II Interpretation of Infrared Spectra (00 pts)

Match the eight compounds that are l sted below wi h cor esponding Inf ared spe tra that are displayed on this page and the next Wri e the let er of your sele t on on the answer sheet (0 pts e ch/00 pts total)

A

B

E

D

C

G

F

H

Part III 1 H NMR spectroscopy

Complete the folowin pro lems in olvin the interpretato of NMR spe tra The mole ular formula is given for e ch spe trum In ad iio , key inf ared f eq encies are given for e ch NMR spe trum Draw the mole ular structure as ociated wih the NMR spe trum o the answer she t pro ided

(0 pts)

Compound A : Mole ular formula = C3H7Br Key Inf ared signal 2987 cm-1

Compound B : Mole ular formula = C4H9Br Key inf ared signal 2982 cm-1

A

3H, t

2H,sextet 2H, t

s = sin let d = d u let t = triplet q = q artet p = pentet m = muliplet

There is no relative integration

B

Compound C : Mole ular formula = C4H9Br . Key inf ared signal 2975 cm-1.

Compound D : Mole ular formula = C5H1 Br , Key inf ared signal 2970 cm-1.

Compound E : Mole ular formula = C4H1 O Key inf ared signals: 3342, 1099 cm-1.

C

Th sig al at 3.8 p m disa p ars

wi h h a di o of D2O.

6H triplet 4H

6H 1H

2H 1H

Compound F : Mole ular formula = C5H1 O Key Inf ared signal 3386 cm-1(broad)

Compound G : Mole ular formula = C9H1 Key Inf ared signal 3082, 749, 699 cm-1

Compound H : Mole ular formula = C5H1 O Inf ared signal 2874, 2719, 1726 cm-1

F The signal at 2.0 ppm disappears with the addition of D2O 9H, s

2H, s

1H, s

2H, sextet 2H, t

5H, m

2H, t

2H, pentet

2H, sextet 1H, singlet

Compound I : Mole ular formula = C3H6O2 IR signal 3020 (broad), 1703 cm-1

Compound J : Mole ular formula = C1 H1 O2: IR signal 3001 (broad), 1701, 1192 cm-1

3H, t

2H, quartet 1H, bro d singlet

I

1H, bro d singlet

Mole ular formula = C6H1 Cl,Key IR sig als: 29 6 cm-1.

Mole ular formula = C1 H1 O2,Key IR sig als: 3 7 ,2 2 ,1 1 ,1 4 cm-1

6H, singlet

1 H, multiplet

6H, d

3H, t 3H, s

2H, q

1 Calculate the chemical shifts for each of the carbons in the following molecule Place your answers on the line after the appropriate carbon atom A correct answer should be precise to one decimal place (e.g 128.5; NOT 129 ppm)

Your answers must match the correct answer within +/– 0.5 ppm

You may use the area below for scratch work, but it will not be graded

2 Calculate the chemical shifts for each of the labeled protons in the following molecules Place your answers on the line after the appropriate atom A correct answer should be precise to two decimal places (e.g 5.25 ppm; NOT 5.3 ppm)

Your answers must match the correct answer within +/– 0.05 ppm

(12 points total)

You may use the area below for scratch work, but it will not be graded

H a H b

H O

4 Elucidate the following structure based on the 13 C NMR data

a) Calculate the IHD: _ (1 pt)

c) Circle the substructure that is associated with the following 13 C NMR resonances If none of the below functional groups exist, then circle “none

of the above” (6 points)

145.3 d

112.6, t

b) How many hydrogens are on carbons? _ (1 pt)

substituted alkene

mono- disubstituted alkene trans-disubstituted

cis-alkene

trisubstituted alkene tetrasubstitutedalkene

N O

amide

R2N

C terminal alkyne

internal alkyne

OH

primary alcohol secondaryalcohol

OH

tertiary alcohol

OH

NH2primary amine secondaryamine

H N

tertiary amine N

none of the above

O

ketone

1,4-disubstituted benzene

monosubstituted

benzene trisubstitutedbenzene

d) Indentify the functional group associated with 72.5, s

If the correct functional group is not listed, then circle “none of the above” (6 points)

e) Draw the structure (11 points)

4 Elucidate the following structure based on the 13 C NMR data

cis-alkene

trisubstituted alkene tetrasubstitutedalkene

OH

primary alcohol secondaryalcohol

OH

tertiary alcohol

OH

NH2primary amine secondaryamine

H

tertiary amine N

none of the above

O

ketone

1,4-disubstituted benzene

monosubstituted

benzene 1,3-disubstitutedbenzene 1,2-disubstituted

benzene trisubstitutedbenzene

5 Elucidate the following structure based on the 1 H and 13 C NMR data (continued)

a) Calculate the IHD: _ (1 pt)

b) How many hydrogens are on carbons? _ (1 pt)

c) Identify the substructure that is associated with the following (6 pts)

197 (s)

substituted alkene

mono- disubstituted alkene trans-disubstituted

cis-alkene

trisubstituted alkene tetrasubstitutedalkene

OH

primary alcohol secondaryalcohol

OH

tertiary alcohol

OH

NH2primary amine secondaryamine

H N

tertiary amine N

O

ketone

1,4-disubstituted benzene

monosubstituted

benzene trisubstitutedbenzene

5 Elucidate the following structure based on the 1 H and 13 C NMR data

d) Identify the substructure that is associated with the following (7 points)

e) Draw the structure (18 points)

substituted alkene

mono- disubstituted alkene trans-disubstituted

cis-alkene

trisubstituted alkene tetrasubstitutedalkene

amide

R2N

C

terminal alkyne

C H C C

internal alkyne

OH

primary alcohol secondaryalcohol

OH

tertiary alcohol

OH

NH2

primary amine secondaryamine

H

tertiary amine N

none of the above

O

ketone

1,4-disubstituted benzene

monosubstituted benzene 1,3-disubstitutedbenzene 1,2-disubstituted

benzene trisubstitutedbenzene

2 Explain how you would use 1H NMR spectroscopy to distinguish the following compounds.You may use chemical structures to support your answer, but use no more than 30 words.

3 Explain how you would use IR spectroscopy to distinguish the following compounds.You may use chemical structures to support your answer, but use no more than 30 words

Br

Br

O HO

OH O

for answers: see Chem 334, 2009, exam 2: http://www.udel.edu/chem/fox/chem334Spring2009.html

a) Circle the functional group that is associated with

(i) IR: 1692 cm-1

H O

O

NR2

O Cl

R R

R R

R R

O

aromatic ketone

O H

!,"-unsaturated aldehyde

O H

aromatic aldehyde

O

RO

O RO aliphatic

ester !,"-unsaturated

ester

O RO

aromatic ester

3 Elucidate the following structure

b) draw the structure of the product (no partial credit)

c Assign the following coupling constants:

2 Elucidate the following structure

C 11 H 13 NO 3

208.2 (s) 148.5 (s) 135.4 (d) 135.2 (s) 129.5 (d)

31.0 (t) 48.4 (d)

7.9 (q) 15.8 (q)

124.4 (d) 122.0 (d)

8.05 (t, J=2.1 Hz, 1H) 8.01 (dt, J=7.9, 2.1 Hz, 1H) 7.51 (dt, J=7.9, 2.1 Hz, 1H) 7.47 (t, J=7.9 Hz, 1H) 3.81 (q, J=6.8 Hz, 1H) 2.49 (m, 2H)

1.44 (d, J=6.8 Hz, 3H) 1.06 (t, J=7.0 Hz, 3H)

a) Circle the functional group that is associated with

(i) IR: 1520 and 1350 cm-1 (both peaks are associated with one functional group)

O alkyl alkyl

O Cl alkyl

R R

R R

R R

ether alcohol amine alkyl chloride

alkylamide alkyl acid chloride

alkyl carboxylic acid

O alkyl Ar

mono-arylketone

alkyl CNalkylnitrile arylnitrile

aryl CNO

Ar Ar diarylketone

arylaldehyde

O H Ar

note: "Ar" refers to aryl, or an aromatic ring

O

NR2Ar

arylamide

O Cl Ar aryl acid chloride

O aryl HO

aryl carboxylic acid

O alkyl RO

alkyl carboxylic ester

O aryl RO

aryl carboxylic ester