1. Chapter 14 NMR: Connectivity
Organic Chemistry II
Fall 2005
Chapter 14 NMR: Connectivity
nuclear magnetic resonance (NMR): theory
information: d, multiplicity, integral;  544 Figure 14.1
nuclear spin (1H & 13C)nuclear magnetic moment (m)
external field: DE = hgBo/2p,  545 Figure 14.2
different 1H with different e- density: different resonance
electronic spin  local magnetic field (opposite to Bo)
chemical shift (d): ppm (Me4Si),  548 Figure 14.4
lower n -downfield-deshielded / higher n -upfield-shielded
OrgChem-Chap14
Chapter 14

2. Factors on Chemical Shift (d )
Organic Chemistry II
Fall 2005
Factors on Chemical Shift (d )
inductive effects:  549
Y-C-H: downfield with electronegative Y
p-electron effects: anisotropic effect,  549
H-C(O) > H-CAr > H-Csp2 > H-Csp:  550 top
exchangeable protons: O-H/N-H (H-bonding)
O-H: 2~5 (ppm), N-H: 1~3, CO2H: ~12 (10~15)
OrgChem-Chap14
Chapter 14

3. Chemical Shift Equivalence
Organic Chemistry II
Fall 2005
Chemical Shift Equivalence
chemically equivalent: interchangeable
identical substitution results:  550 bot
enantiotopic & diastereotopic:  551
practice:  552 Problem 14.1 & 14.2
estimation of d :  553 & 554 Table 14.1
increments: CH ppm; CH +0.7; 2nd a-group +(d -0.9); b-group +0.3
practice:  & 556 Prac. Prob. 14.2
OrgChem-Chap14
Chapter 14

4. Coupling Constant (J): Connectivity
Organic Chemistry II
Fall 2005
Coupling Constant (J): Connectivity
spin coupling: change in the local magnetic field by nearby H atoms having different d
multiplicity: Bo  BH;  557~8 & Figure
splitting pattern: JAX in 0~20 Hz (typical); s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), br (broad)
splitting with non-equivalent Hs:  560
leaning: Hs with close d ;  562 Figure 14.8
proximity: the reach of local BH ;  557 top
practice:  561, Problem 14.4~6
OrgChem-Chap14
Chapter 14

5. Interpretation of 1H NMR Spectra
Organic Chemistry II
Fall 2005
Interpretation of 1H NMR Spectra
deuterated solvents: CDCl3, (CD3)2SO, C6D6
chemical exchange: average d
conformation: cyclohexane; chair (He) chair (Ha)
H (D) exchange: O-H / N-H,  563 middle
carbocations by NMR:  565 Focus On
NMR in medicine: MRI;  574 Focus On
partial structure:d , multiplicity, integral
practice:  567~573, Fig & Prob. 14.8
OrgChem-Chap14
Chapter 14

6. 13C NMR Spectra d range: 0~220 ppm;  576 middle
Organic Chemistry II
Fall 2005
13C NMR Spectra
d range: 0~220 ppm;  576 middle
 577 Table 14.2 &  575 Figure 14.11
coupling: 13C-H (1JCH ~ 3JCH) [no 13C -13C]
natural abundance: 13C 1.1% & 12C 98.9%
decoupling: broadband (BB) & off-resonance
DEPT 13C-NMR:  579 Figure 14.12
OrgChem-Chap14
Chapter 14

7. Interpretation of 13C NMR Spectra
Organic Chemistry II
Fall 2005
Interpretation of 13C NMR Spectra
integration: usually not proportional
No. of carbons: symmetry of molecules
practice:  580~1 Figure 14.13~14 &  582~3 Problem 14.11
OrgChem-Chap14
Chapter 14

8. Structure Identification: IR & NMR
Organic Chemistry II
Fall 2005
Structure Identification: IR & NMR
molecular formula: degree of unsaturation
IR: functional groups
1H & 13C NMR: CmHn fragments, functional groups, connectivity (- CmHn-CoHp-)
tentative structure & double check!!
practice:  585~7 Figure 14.15~16 &  587~95 Problems 14.12~14
OrgChem-Chap14
Chapter 14