Applications of solid state NMR to the study of molecular structure.
Date
1990
Authors
Curtis, Ronald Dean.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
This thesis illustrates several applications of dilute spin I = $1\over2$ solid state nmr spectroscopy to the study of molecular structure in systems of chemical interest. Specifically, the compounds studied include benzylideneaniline and several related imines, the first stable iminophosphenium cation containing a N,P triple bond and several tetracyclines.
The first two applications describe the use of dipolar-chemical shift nmr of "isolated" spin-pairs to fully characterize chemical shift tensors. For example, the carbon and nitrogen shift tensors of the C=N linkage of the Schiff base benzylideneaniline have been completely specified. The most shielded principal component of both carbon and nitrogen shift tensors is approximately perpendicular to the imine fragment. For the imine carbon, the intermediate component of the shift tensor is directed approximately along the C=N bond whereas the corresponding component of the nitrogen shift tensor is oriented along the direction of the nitrogen lone pair. Examination of the nitrogen chemical shift parameters for several related imines suggests that variations in the least shielded principal component are mainly responsible for changes in the nitrogen shieldings in the imine system. For the N,P moiety of the iminophosphenium cation, the most shielded principal component of both nitrogen and phosphorus tensors is oriented along the N,P bond axis. Comparison of both shift tensors with those of related compounds suggests that the electronic environment surrounding the N,P moiety is similar to other systems containing a formal triple bond.
The final application section demonstrates the utility of high-resolution $\sp $C and $\sp $N cp/mas nmr for studying the molecular structure of solid tetracycline antibiotics. Comparison of $\sp $C chemical shifts in the solid state to those determined in (CD$\sb3)\sb2$SO solutions indicates for the first time that the structural integrity of the A ring of the tetracyclines is maintained in solution.
Thesis (Ph.D.)--Dalhousie University (Canada), 1990.
The first two applications describe the use of dipolar-chemical shift nmr of "isolated" spin-pairs to fully characterize chemical shift tensors. For example, the carbon and nitrogen shift tensors of the C=N linkage of the Schiff base benzylideneaniline have been completely specified. The most shielded principal component of both carbon and nitrogen shift tensors is approximately perpendicular to the imine fragment. For the imine carbon, the intermediate component of the shift tensor is directed approximately along the C=N bond whereas the corresponding component of the nitrogen shift tensor is oriented along the direction of the nitrogen lone pair. Examination of the nitrogen chemical shift parameters for several related imines suggests that variations in the least shielded principal component are mainly responsible for changes in the nitrogen shieldings in the imine system. For the N,P moiety of the iminophosphenium cation, the most shielded principal component of both nitrogen and phosphorus tensors is oriented along the N,P bond axis. Comparison of both shift tensors with those of related compounds suggests that the electronic environment surrounding the N,P moiety is similar to other systems containing a formal triple bond.
The final application section demonstrates the utility of high-resolution $\sp $C and $\sp $N cp/mas nmr for studying the molecular structure of solid tetracycline antibiotics. Comparison of $\sp $C chemical shifts in the solid state to those determined in (CD$\sb3)\sb2$SO solutions indicates for the first time that the structural integrity of the A ring of the tetracyclines is maintained in solution.
Thesis (Ph.D.)--Dalhousie University (Canada), 1990.
Keywords
Chemistry, Analytical., Physics, Molecular.