Determination and analysis of nJch (n=2,3,4) coupling constants in norbornane derivatives / Determinação e analise das constantes de acoplamento nJch (n=2,3,4) em derivados do norbornano

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

In the introduction, it is presented a discussion about the effect of hyperconjugative interactions on coupling constants and a discussion about some methodologies for the measurement of long range heteronuclear coupling constants. The reader is introduced to the topics which are the basis of this thesis. Then it is presented the results of the measurement of coupling constants JCH, with special emphasis on HSQMBC experiments and the spin state selective methodologies (HSQC-TOCSY-IPAP and HSQC-TOCSY-IPAP-triple editing). After that, a rationalization of the known difference between the JC4H1 and JC1H4 coupling constant 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 JC4H couplings were carried out for 3-endo- and 3-exo-X-2-norbornanone (X = Cl, Br, SCH3) and for exo- and endo-2- norbornanes derivatives. The hyperconjugative interactions were studied with the Natural Bond Orbital (NBO) analyses. It was observed that interactions involving the carbonyl p*C2=O and s*C2=O antibonding orbitals produce a decrease of threebond contribution for o both JC4H1 and JC1H4 couplings. However, the latter antibonding orbital also undergoes a strong sC3-C4s*C2=O interaction, which defines an additional coupling pathway for JC4H1 but not for JC1H4 .This pathway is similar to that known for homoallylic couplings, being the only difference the nature of the intermediate antibonding orbital, i.e. for JC4H1 is of s-type, while in homoallylic couplings is of p-type.

ASSUNTO(S)

sequencia de pulsos constante de acoplamento pulse sequence ressonancia magnetica nuclear nuclear magnetic resonance coupling constante

ACESSO AO ARTIGO

Documentos Relacionados