| Popis: |
Publisher Summary This chapter examines the carbon–proton coupling constants involved in the conformational analysis of sugar molecules. The indirect spin–spin coupling is independent of molecular rotation. The coupling mechanism is known to involve the electron spins of the bonding electrons and is the result of a weak electron polarization. A proton signal has two 13C satellites, each having an intensity that is 0.5% of that of the corresponding total proton resonance and located symmetrically around that resonance. In addition to providing information about 1H ( 1H couplings) these satellites allow the determination of the 1JC,H couplings with good resolution. With the advent of inverse detection and the corresponding gain in sensitivity, newer schemes for the measurement of long-range coupling constants have been proposed. They are based on the heteronuclear multiple-bond correlation derivative or variants of the heteronuclear multiple-quantum coherence experiment, and also on the heteronuclear single-quantum coherence experiment. The Hamiltonian gives the total electronic kinetic energy and the magnetic interactions between electron orbital motions and nuclear magnetic moments. It is found that two-bond carbon–proton coupling constants are much smaller than one-bond couplings and their signs can be negative or positive. |
