ISSN:
0170-2041
Keywords:
Aryl group, rotation
;
Cuprates
;
Diastereotopomerization
;
Hydrazones
;
Styrene derivatives
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Two series of new compounds with sterically shielded, sp2-hybridized C-α atoms are prepared from bromo(chloro)-2,6-diisopropylbenzene. The α-(2,6-diisopropylphenyl) substituent common to all of them is used as an NMR-spectroscopic indicator for the ease of aryl-α single-bond rotation. The corresponding ΔG≠ values are 〉23.8 kcal/mol with methyl or bromine as additional α substituents at a C=C bond, but 〈8.5 kcal/mol with α-H. The analogous 2,6-diisopropylacetophenone imine has ΔG* = 18.0 kcal/mol while the N-substituted imines prefer the (Z) conformations with ΔG≠ 〉 23.3 kcal/mol, and ΔG≠ ≈ 31.5 kcal/mol for the (Z)-hydrazone. Comparisons of these data with reaction conditions show that chemical transformations are not seriously impeded unless they depend on reagent attack at a π face of the C-α atom in a C=C or C=N group which rotates slowly about the bond to 2,6-diisopropylphenyl.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199419940417
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