13 C NMR 13 C has 1.1 % natural abundance 13 C NMR is not very - - PowerPoint PPT Presentation

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May 01, 2023 178 likes •332 views

13 C NMR 13 C has 1.1 % natural abundance 13 C NMR is not very sensitive! 13 C - 13 C spin-spin splitting is never observed almost no molecules have 2 13 C in them: for example, the probability of hexane having two adjacent 13 C is

SLIDE 1

13C NMR

13C has 1.1 % natural abundance 13C NMR is not very sensitive! 13C - 13C spin-spin splitting is never observed

almost no molecules have 2 13C in them: for example, the probability of hexane having two adjacent 13C is 0.011 x 0.011 x 0.29 = 3.5 x 10 -6

13C NMR is a carbon counter

tells you the number of chemically nonequivalent carbons carbons appear in a 0 - 200 ppm region

13C NMR spectra normally are not integrated

peak intensities can be used to guess the “type” of carbon: usually, CH3 > CH2 > CH > C

SLIDE 2

DEPT 13C NMR spectrum

tells you the number of chemically nonequivalent CH3 , CH2 , and CH carbons C do not appear–they must be identifed by comparison with the normal 13C NMR spectrum ways to present a DEPT 13C NMR spectrum:

Q (13C NMR spectrum) + (DEPT-90) + (DEPT-135)

(all carbons) + (only CH carbons) + (CH and CH3 carbons up, CH2 carbons down) this is the textbook’s method

Q (13C NMR spectrum) + (CH3 subspectrum) + (CH2 subspectrum) + (CH subspectrum)

+ (all protonated carbons subspectrum)

Q 13C NMR spectrum with CH3 , CH2 , CH , and C resonances labeled

SLIDE 3

13C NMR methanol

SLIDE 4

13C NMR ethanol

SLIDE 5

13C NMR ethyl acetate

SLIDE 6

BASIC 13C NMR CHEMICAL SHIFTS C Type

Approximate , ppm Alkanes Methyl 0 - 30 Methylene 15 - 55 Methine 25 - 55 Quaternary 30 - 40 Alkenes C= C 80 - 145 Alkynes CC 70 - 90 Arenes 110 - 170 Benzene 128.7 Alcohols and Ethers C–O 50 - 90 Amines C–N 40 - 60 Halogens C–F 70 - 80 C–Cl 25 - 50 C–Br 10 - 40 C–I

20 - 10

Carbonyls R2C= O 190 - 220 RXC= O (X = O or N) 150 - 180

SLIDE 7

13C NMR of a tribromobenzene, C6H3Br3

What’s the structural formula?

SLIDE 8

13C NMR of 1,3,5-tribromobenzene

SLIDE 9

13C NMR spectrum of a chloropentane

SLIDE 10

Use of DEPT 13C NMR to identify chloropentane structural isomers A C5H11Cl

SLIDE 11

Use of DEPT 13C NMR to identify chloropentane structural isomers CH2 CH2 CH2 CH3 CH2 A C5H11Cl

SLIDE 12

Use of DEPT 13C NMR to identify chloropentane structural isomers CH2 CH CH3 CH2 CH3 B C5H11Cl

SLIDE 13

Use of DEPT 13C NMR to identify chloropentane structural isomers CH2 CH2 CH3

CH3

C C5H11Cl CH

SLIDE 14

Use of DEPT 13C NMR to identify chloropentane structural isomers CH3 CH2 D C5H11Cl CH3 C

SLIDE 15