Premium
Computation and analysis of 19 F substituent chemical shifts of some bridgehead‐substituted polycyclic alkyl fluorides
Author(s) -
Adcock William,
Peralta Juan E.,
Contreras Ruben H.
Publication year - 2003
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.1202
Subject(s) - natural bond orbital , chemistry , electronegativity , antibonding molecular orbital , lone pair , substituent , computational chemistry , chemical shift , molecular orbital , molecular geometry , fluorine , crystallography , density functional theory , stereochemistry , molecule , atomic orbital , organic chemistry , electron , physics , quantum mechanics
The 19 F NMR shieldings for several remotely substituted rigid polycyclic alkyl fluorides with common sets of substituents covering a wide range of electronic effects were calculated using the DFT‐GIAO theoretical model. The level of theory, B3LYP/6–311+G(2d,p), was chosen based on trial calculations which gave good agreement with experimental values where known. The optimized geometries were used to obtain various molecular parameters (fluorine natural charges, electron occupancies on fluorine of lone pairs and of the CF bond, and hybridization states) by means of natural bond orbital (NBO) analysis which could help in understanding electronic transmission mechanisms underlying 19 F substituent chemical shifts (SCS) in these systems. Linear regression analysis was employed to explore the relationship between the calculated 19 F SCS and polar substituent constants and also the NBO derived molecular parameters. The 19 F SCS are best described by an electronegativity parameter. The most pertinent molecular parameters appear to be the occupation number of the NBO p‐type fluorine lone pair and the occupation number of the CF antibonding orbital. This trend suggests that in these types of rigid saturated systems hyperconjugative interactions play a key role in determining the 19 F SCS. Electrostatic field effects appear to be relatively unimportant. Copyright © 2003 John Wiley & Sons, Ltd.