ISSN:
0749-1581
Keywords:
Hindered rotation
;
1H and 13C relaxation measurements
;
Molecular mechanics calculations
;
NOE experiments
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A collection of cis- and trans-9-isopropyl-10-R-9,10-dihydroanthracenes were investigated. The cis compounds show large H-9-isopropyl methine coupling constants in the series R — Me, Et, i-Pr, t-Bu (8.8-9.9 Hz) due to a preferred orientation of the isopropyl group(s), caused by a transannular steric effect, wherein the H-9 - isopropyl methine dihedral angle is close to 180°. These preferred conformations are predicted by molecular mechanics calculations (MM2 and MMP2) and data for the optimized geometries are presented. The trans compounds show considerably smaller coupling constants (J = 2.6, 5.0 and 7.8 Hz for R = t-Bu, i-Pr and Et, respectively) and these numbers are easily rationalized from the calculated geometries. However, the compound with R — Me shows an unusually high value (9.6 Hz), and calculations suggested the presence of a structure with unusually large puckering of the dihydroanthracene central ring. This was confirmed by nuclear Overhauser enhancements and by proton and carbon relaxation measurements.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260270219
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