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

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

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: CH2 +0.3 ppm; CH +0.7; 2nd a-group +(d -0.9); b-group +0.3 practice:  554-5 & 556 Prac. Prob. 14.2 OrgChem-Chap14 Chapter 14

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 14.6-7 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

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. 14.9-10 & Prob. 14.8 OrgChem-Chap14 Chapter 14

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

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

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