(BQ) Part 2 book A Handbook of spectroscopic data chemistry has contents: 13C NMR spectroscopy, mass spectrometry, structural data obtainable from different spectra. Please refer to the content. (BQ) Part 2 book A Handbook of spectroscopic data chemistry has contents: 13C NMR spectroscopy, mass spectrometry, structural data obtainable from different spectra. Please refer to the content.
4 13e NMR Spectroscopy 4.1: The 13C chemical shifts of Linear and Branched Alkanes: Alkane groups unsubstituted by heteroatoms absorb downfield from TMS to about 60 ppm (Methane absorbs at 2.5 ppm upfield from TMS.) Within this range we can predict the chemical shifts of individual 13C atoms in a straight chain or branched chain hydrocarbon from the data in Table 4.1 and the formula b = -2.5 + LnA Where b = Predicted shift for a carbon atom A = Additive shift parameter n = number of carbon atoms for each shift parameter (-2.5 is the shift of the i3C of methane) The calculated (and observed) shifts for the carbon atoms of 3-methylpentane are /+ 19.3 (18.6) CH I I CH - I + 11.3 (+11.3) CH - CH- CH - \ +29.5 (+29.3) " + 36.2 (+ 36.7) CH 100 Spectroscopic Data Chemistry For carbon atom I, we have la, ° =-2.5 + (9.1 x I) + (9.4 x I~-, 2y and 1&-carbon atoms I) + (-2.5 x 2) + (0.3 x I) = + 11.3 Carbon atom has a-, ~-, and y carbon atoms Carbon atom is a 2° carbon with a 3° carbon attached [2°(3°) = - 2.5] ° =-2.5 + (9.1 x 2) + (9.4 x 2) + (-2.5 x 1) + (-2.5 x 1) = 29.5 Carbon atom has a- and ~- carbon atoms, and it is a 3° atom with two 2° atoms attached [3° (2°) = -3.7] Thus 03 = -2.5 + (9.1 + (-3.7 x x 3) + (9.4 x 2) 2) = + 36.2 Carbon atom has, I a-, 2~-, and 2y carbon atoms, and it is a 1° atom with a3° atom attached [10 (3°) =-1.1] Thus, +(-2.5x2)+(-1.l x °=-2.5 +(9.1 x 1)+(9.4 x 2) 1)=+19.3 The agreement for such calculations is very good It is essential that the reference compounds used for such additivity culculations be structurally similar to thecompound of interest Table 4.1: The \3C shift parameters in some linear and branched hydrocarbons 13C Atoms Shift (ppm) (A) a +9.1 p +9.4 Y b -2.5 E +0.1 +0.3 1° (3? -1.1 1° (4°)" 20 (3 o)a -3.4 20 (4°) -7.2 3° (2°) -3.7 3° (3°) -9.5 4° (10) -1.5 ° (2°) -8.4 -2.5 101 I3C NMR Spectroscopy a The notations 1° (3°) and 1° (4°) denote a CH group bound to a R2CH group and to a R3C group, respectively The notation 2° (3°) denotes a RCH group bound to a ~CH group, and so on Table 4.2 lists the shifts in some linear and branched alkanes Table 4.2: The \3C Shifts for some Linear and Branched chian Alkanes (ppm from TMS) Compound C-l C-2 C-3 Methane -2.3 Ethane 5.7 Propane 15.8 16.3 15.8 Butane 13.4 25.2 25.2 Pentane 13.9 22.8 Hexane 14.1 Heptane C-4 C-5 34.7 22.8 13.9 23.1 32.2 32,2 23.1 14.1 23.2 32.6 29.7 32.6 Octane 14.2 23.2 32.6 29.9 29.9 Nonane 14.2 23.3 32.6 30.0 30.3 Decane 14.2 -23.2 32.6 31.1 30.5 Isobutane 24.5 25.4 Isopentane 22.2 31.1 32.0 11.7 lsohexane 22.7 28.0 42.0 20.9 Neopentane 31.7 28.1 2,2-Dimethylbutane 29.1 30.6 36.9 8.9 3-Methylpentane 11.5 29.5 36.9 (18.8,3CH) 2,3-Dimethylbutane 19.5 34.3 2,2,3-Trimethyl 27.4 33.1 38.3 16.1 7.0 25.3 36.3 (14.6,3-CH 3) butane 2,3-Dimethylpentane 14.3 102 Spectroscopic Data Chemistry Table 4.3: Incremental Substituent Effects (ppm) on Replacement ofH by Y in Alkanes Y is Terminal or Internal" (+ downfield, -upfield) y ~y'" ~ Terminal Y a Internal ~ y Terminal Internal Terminal Internal +9 +6 +10 +8 -2 CH3 CH=CH2 +20 +6 -0.5 +4.5 +5.5 -3.5 C=CH +2 COOH +21 +16 +3 -2 COO-2 +25 +20 +5 +3 +2 -2 COOR +20 +17 +3 +33 +28 +2 COCI +22 CONH2 -0.5 +2.5 +30 +24 +1 +1 -2 COR -2 CHO +31 Phenyl +23 +17 +9 +7 -2 +48 +41 +10 +8 -5 OH +58 +51 +8 +5 -4 OR +51 +45 +6 +5 -3 OCOR -5 +29 +24 +11 +10 NH2 -5 NH3+ +26 +24 +8 +6 +8 +6 -4 NHR +37 +31 +42 -3 N~ -7 +31 +5 NR/ +4 +4 N0 +63 +57 +3 -3 +4 +1 +3 CN +11 +11 +12 +11 -4 SH -3 +20 +7 SR -F +6 -4 +9 +68 +63 +31 +32 +11 +10 -4 CI + 11 +20 +10 -3 Br +25 -1 +4 +11 +12 I -6 a Add these increments to the shift values ofthe appropriate carbon atom in Table 4.2 or to the shift value calculated from Table 4.1 From Table 4.3, the approximate shifts for the carbon atoms of, for example, 3-pentanol, may be calculated from the values for pentane in Table 4.2; that I1C NMR Spectroscopy 103 is, the increment for the functional group in Table 4.3 is added to the appropriate value in Table 4.2 as follows: y f3 a CH - CH - CH- CH I f3 y CH OH Ca CI3 Cy Calculated Found 34.7 + 41 = 75.8 22.8 + = 30.8 13.9 - = 8.9 73.8 30.0 10.1 The chemical shifts of the CH groups in monocyclic alkanes are given in Table 4.4 Each ring skeleton has its own set of shfit parameters Rough estimates for substituted rings can be made with the substitution increments in Table 4.3 Table 4.5 presents chemical shifts for several saturated heterocyclics Table 4.4: Chemical shifts of Cycloalkanes (ppm from TMS) C3 H6 C4HS CsHIO C6 HI2 C7H I4 CgH I6 CgH 1S C 1oH20 -2.9 22.4 25.6 26.9 28.4 26.9 26.1 25.3 Table 4.5: Chemical shifts for saturated Heterocyclics (ppm from TMS, neat) Unsubstituted U D 29.7 H N S 39 27.5 18 U 65 12 68.4 31.7 0 S 18 S 22.9 0 N H 72.6 57 47.1 104 Spectroscopic Data Chemistry 24.9 26.6 o 27.7 /' 69.5 25.9 27.8 29.1 N H S Substituted o ~CH3 47.3 / \ 47.6 27.8 47.9 24.4 567 N CH3 48.0 18.1 4.2 Alkenes and Alkynes The Sp2 carbon atoms of alkenes substituted only by alkyl groups, absorb in the range of about 11 0-150 ppm downfield from TMS The double bond has a rather small effect on the shift of the Sp3 carbon in the molecule Calculation of approximate shifts can be made from the following parameters where (a, ~, and y represent substituents on the same end of the double bond as the alkene carbon of interest, and (a', W, and y' represent substituents on the far side a +10.6 ~ +7.2 Y -1.5 a' -7.9 ~' ·-1.8 y' -1.5 Z (cis) correction -1.1 These parameters are added to 123.3 ppm, the shift for ethylene We can calculate the values for cis-3-methyl-2-pentene as follows: a CH3H P a H3 C-CH 0C_3 I I a C = C -CH3 I = 123.3 + (2 x 10.6) + (l x 7.2) + (l x -7.9) - 1.1 = 142.7 ppm a' CH3H W a' H,C-CH Os 0C_2 = 123.3 + (I -< I I C =C a -cI H3 10.6) + (2 x -7.9) + (I x 1.8) l.l = 115.2 ppm The measured values are C-3 = 137.2 and C-2 = 116.8 The agreement is fair The allylic carbon of a (Z) alkene is usually at lower field from that of IlC NMR Spectroscopy lOS an (E) alkene by about 4-6 ppm Alkene carbon atoms in polyenes are treated as though they were alkane carbon substituents on one of the double bonds Thus in calculating the shift ofC-2 in I A-pentadiene, C-4 is treated like a 13spJ carbon atom Representative alkenes are presented in Table 4.6 There are no simple rules to handle polar substituents on an alkene carbon Shifts for several substituted alkenes are presented in Table 4.7 The central carbon atom (=C=) of alkyl substituted allenes absorbs far downfield in the range of about 200-·215 ppm, whereas the terminal atoms (C=C=C) absorb upfield in the range of about 75-97 ppm Table 4.6: Alkene and Cycloalkene Chemical shifts (ppm from TMS) 111 , H2C=CH~ Iic/C~""'Gr~Ci:i2 I".' I·HJ , 11-11 H,C "cH(CI~"at~CH, "XI , ?_~ 1175 t~C" ~rn 1112 ~, CH, - Spectroscopic Data Chemistry 106 J 14 ~ I ~') :; HF, /GI~ ill "CH-CH 1.17 M 13-' 121\.l 127A 123 I J 125 172 12 H IIW H2C, /CH,,,,,- /C~ C CH: 1';·15 I CIt ' CH, I 1129 H~C~I/GI"'-cI-~CH3 1.;49 107.1 CH2 /~.7 130.8 137.2 0-',-6 22.1 :- I ~ 124.6 22.3 CH,=C=CH, 74 X :: I ~ " 136 ~ ./)2g.9 26.9 107 IlC NMR Spectroscopy Table 4.7: Chemical Shifts of substituted Alkenes (ppm from TMS) 1220 I~C.-;7 12f1 I or, a-I, I~C~ 'Br 11