物理有机化学习题1.pdf

物理有机化学习题物理有机化学习题1 1 Use thermochemical relationships to obtain the required information a The heats of formation of cyclohexane cyclohexene and benzene are respectively 29 5 1 1 and 19 8 kcal mol Estimate the resonance energy of benzene using these data b Calculate H for the air oxidation of benzaldehyde to benzoic acid given that the heats of formation of benzaldehyde and benzoic are 8 8 and 70 1 kcal mol respectively 提示 略提示 略 2 Suggest an explanation for the following observations a The dipole moment of the hydrocarbon calicene has been estimated to be as large as 5 6 D H Prinzbach Pure Appl Chem 28 281 1971 提示 提示 b The dipole moment of furan is smaller than and in the opposite direction from that of pyrrole ON H T J Baton R W Roth and J G Verkade J Am Chem Soc 94 8854 1972 提示 共轭体系形成及元素电负性提示 共轭体系形成及元素电负性 3 Predict the energetically preferred site of protonation for each of the following molecules and explain the basis of your prediction C6H5HCN N H C6H5 C O CH3 NHCH3 N NH2 R L Reeves and W F Smith J Am Chem Soc 85 724 1963 R B Martin J Chem Soc Commun 793 1972 J A Joule and G F Smith Heterocyclic Chemistry Van Nostrand Reinhold London 1972 c pp194 195 d p 64 提示 元素电负性及电荷分布状况提示 元素电负性及电荷分布状况 4 What physical properties such as absorption spectra bond length dipole moment etc could be examined to obtain evidence of resonance interactions in the following molecues What deviations from normal physical properties would you expect to find N C6H5 O C6H5C6H5 CHCCH3 O H L Ammon and G L Wheeler J Am Chem Soc 97 2326 1975 R Breslow T Eicher A Krebs R A Peterson and J Posner J Am Chem Soc 87 1320 1965 R B Woodward J Am Chem Soc 97 1123 1941 提示 略提示 略 5 Certain C H bonds have significantly lower bond dissociation energies than do the nomal C H bonds in saturated hydrocarbons Offer a structural rationalization of the lowered bond energy in each of the following compounds relative to the saturated hydrocarbon C H bond taken as a reference the bond dissociation energies are given in kcal mol CH2H 85 versus CH3H 103 HOCH2H 92 versus CH3H 103 H3CCH 88 versus CH3CH2 O H 98 R T Sanderson J Am Chem Soc 97 1367 1975 提示 元素电负性及轨道对称性对成键强度的影响提示 元素电负性及轨道对称性对成键强度的影响 6 a Carboxamides have substantial rotational barriers on the order of 20 kcal mol for the process RC N O RC O CH3 CH3 NCH3 CH3 Develop a structural explanation for the existence of this barrier in both resonance and molecular orbital terminology 提示 提示 RC N O CH3 CH3 b In the gas phase the rotational barrier of N N dimethylformamide is about 19 4 kcal mol which is about 1 5 kcal mol less than in solution Is this change consistent with the ideas you presented in a Explain B B Ross and N S True J Am Chem Soc 106 2451 1984 提示 溶剂化的稳定作用提示 溶剂化的稳定作用 c Explain the relative rates of alkaline hydrolysis of the following pairs