N-H and alpha(C-H) bond dissociation enthalpies of aliphatic amines
Lalevée, J; Allonas, X; Fouassier, JP
| HERO ID | 4182379 |
|---|---|
| In Press | No |
| Year | 2002 |
| Title | N-H and alpha(C-H) bond dissociation enthalpies of aliphatic amines |
| Authors | Lalevée, J; Allonas, X; Fouassier, JP |
| Journal | Journal of the American Chemical Society |
| Volume | 124 |
| Issue | 32 |
| Page Numbers | 9613-9621 |
| Abstract | Bond dissociation enthalpies (BDEs) of a large series of aliphatic amines (21) were measured by means of photoacoustic calorimetry. Despite the different structures studied in the primary, secondary, and tertiary amine series, the alpha(C-H) BDEs were found to be very similar for unconstrained amines with values very close to 91 kcal/mol. alphaC- and N-alkylation or introduction of an hydroxy group only slightly affect the BDEs, a fact in perfect agreement with calculations performed at different CBS levels. This demonstrates the predominance of the two-orbital-three-electron interaction involving the N and alphaC(*) orbitals. On the other hand, the N-H BDE decreases when going from primary to secondary amines. This result is interpreted in term of a hyperconjugation in sigmaC-C bonds, which leads to a stabilization of the aminyl radical. For cyclized amines, the BDEs depend on the relative geometry of the singly occupied alphaC(*) orbital with respect to that of the N atom, disfavoring the two-orbital-three-electron interaction. However, such structures can exhibit through-bond interaction. For a crowded structure such as triisopropylamine, for which the alphaC(*) orbital is not coplanar with the nitrogen one, the relaxation of a strain energy allows the BDE to be comparable to flexible structures. |
| Doi | 10.1021/ja0204168 |
| Pmid | 12167057 |
| Wosid | WOS:000177358600060 |
| Is Certified Translation | No |
| Dupe Override | No |
| Is Public | Yes |
| Language Text | English |