CHAPTER 15: ANSWERS TO PRACTICE PROBLEMS
1. The C=N bond is intermediate in polarity between the C=O and C=C bonds, because nitrogen is intermediate between O and C in electronegativity. Therefore the ionic resonance form of the C=N bond contributes more to the resonance hybrid than in the case of the C=C but less than in the C=O. The stabilization provided by the ionic resonance structure is then intermediate between the carbonyl and alkene double bonds. The hybridization of both N and C is sp2 and the unshared pair of N is also in an sp2 AO (note: the 2 should be superscript).
2.See the illustration below.
3.The character which provides the most direct insight into this question is anionic character. In the reactant Grignard reagent the anionic character is carbanionic, but in the product the anionic character is alkoxide character (oxyanion character). The latter is obviously much more favorable, making the product side more stable than the reactant side. Thus, although some additions to carbonyl groups are thermodynamically unfavorable (such as hydration), the additions of Grignards (and also hydride reagents) is favorable.
4.The choice for preparing 3-heptanol would be preparing a Grignard reagent from 1-bromobutane and adding that to propanal, followed by acidic aqueous workup.For making 2-methyl- 1-phenyl-1-propanol, prepare the Grignard reagent from bromobenzene and add that to 2-methylpropanal, followed by acidic aqueous workup.