Sterically Congested Molecules, 11. The 2,6-Diisopropylphenyl Substituent at CC and CN Groups

✍ Scribed by Knorr, Rudolf ;Ruhdorfer, Jakob ;Böhrer, Petra ;Bronberger, Hildegard ;Räpple, Edith

• Book ID: 102901968
• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 742 KB
• Volume: 1994
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199419940417

✦ Synopsis

Abstract

Two series of new compounds with sterically shielded, sp^2^‐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. magnified image