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The effect of carbonyl group in the asymmetry of 3, 4 J CH coupling constants in norbornanones
Author(s) -
dos Santos Francisco P.,
Tormena Cláudio F.,
Contreras Rubén H.,
Rittner Roberto,
Magalhães Alvicler
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2154
Subject(s) - antibonding molecular orbital , chemistry , natural bond orbital , hyperconjugation , non bonding orbital , atomic orbital , coupling constant , pi bond , computational chemistry , crystallography , stereochemistry , asymmetry , molecular orbital , molecular orbital diagram , bond order , molecular orbital theory , molecule , physics , bond length , electron , density functional theory , quantum mechanics , organic chemistry , crystal structure
A rationalization of the known difference between the 3, 4 J C 4 H 1and 3, 4 J C 1 H 4couplings transmitted mainly through the 7‐bridge in norbornanone is presented in terms of the effects of hyperconjugative interactions involving the carbonyl group. Theoretical and experimental studies of 3, 4 J CH couplings were carried out in 3‐ endo ‐ and 3‐ exo ‐X‐2‐norbornanone derivatives (X = Cl, Br) and in exo ‐ and endo ‐2‐noborneol compounds. Hyperconjugative interactions were studied with the natural bond orbital (NBO) method. Hyperconjugative interactions involving the carbonyl π* C 2 Oand σ* C 2 Oantibonding orbitals produce a decrease of three‐bond contribution to both 3, 4 J C 4 H 1and 3, 4 J C 1 H 4couplings. However, the latter antibonding orbital also undergoes a strong σ C 3 C 4→ σ* C 2 Ointeraction, which defines an additional coupling pathway for 3, 4 J C 4 H 1but not for 3, 4 J C 1 H 4. This pathway is similar to that known for homoallylic couplings, the only difference being the nature of the intermediate antibonding orbital; i.e. for 3, 4 J C 4 H 1it is of σ*‐type, while in homoallylic couplings it is of π*‐type. Copyright © 2007 John Wiley & Sons, Ltd.