Evans. Breit Conformational Analysis: Cyclic Systems-7 Chem 206 Heteroatom-Substituted 6-Membered Rings A-Values for N-Substituents in Piperidine L A-values at the 2-position in both the o&n heterocycles are larger thar expected. This is due to the shorter C-o(1.43 A), and c-N (1.47 A) bond lengths relative to carbon(C-C: 1.53 A). The combination of bond length and bond angle change increases the indicated 1, 3-diaxial interaction(see eq 1, 4) △G°=036 kcal/mol Me Reference NMe-△G°=174 kcal/mol -△G°=30 kcal/mo a Hydrogen is"bigger"than the N-lone Pair a The A-value of N-substituents is slightly larger than the corresponding Me-△G°=286 kcal/mol cyclohexane value. Rationalize e-△G°=143 carmol △G°=40 kcal/mol △=-1kam 6以一公 Me-△G°=25 kcal/mol I The indicated distance is 2. A. The analogous H-H distance in Cyclohexane is 2.45A G°=16 kcal/mol (6) NMe-△G°=19 kcal/mol 2.05A 245AMe H O Me H H O Me H O Me H N Me H H H N Me H H N Me H H H Me N H Me H O H Me N H Me H O H Me O H Me N H Me H O O H Me N Me N H O O Me H O O Me H O O H Me N Me N H Evans, Breit Conformational Analysis: Cyclic Systems-7 Chem 206 Heteroatom-Substituted 6-Membered Rings -DG° = 1.74 kcal/mol Reference: G° = 2.86 kcal/mol -DG° = 1.43 kcal/mol -DG° = 1.95 kcal/mol G° = 2.5 kcal/mol -DG° = 1.6 kcal/mol -DG° = 1.9 kcal/mol A-Values for N-Substituents in Piperidine -DG° = 0.36 kcal/mol The Reference: -DG° = 3.0 kcal/mol ■ Hydrogen is "bigger" than the N–lone Pair. ■ The A-value of N–substituents is slightly larger than the corresponding cyclohexane value. Rationalize -DG° = 4.0 kcal/mol -DG° = 0.8 kcal/mol ■ The indicated distance is 2.05 Å. The analogous H–H distance in Cyclohexane is 2.45 Å (1) (2) (3) (4) (5) (6) 2.05 Å 2.45 Å ■ A-values at the 2-position in both the O & N heterocycles are larger than expected. This is due to the shorter C–O (1.43 Å), and C–N (1.47 Å) bond lengths relative to carbon (C–C; 1.53 Å). The combination of bond length and bond angle change increases the indicated 1,3-diaxial interaction (see eq 1, 4)