Structural study of 2,4,6-triisopropylbenzenesulfonyl chloride

Abstract

The structure of 2,4,6-triisopropylbenzenesulfonyl chloride (TPSCl) (I) was studied by X-ray diffraction. Compound I is a highly selective condensing agent first suggested by Khorana for the formation of the C3′–C5′ interribonucleotide linkage in the oligo- and polyribonucleotide synthesis. I crystals are orthorhombic. At −120°C, the unit-cell parameters are a = 14.184(4) A, b = 11.344(5) A, c = 19.883(6) A, V = 3199(2) A3, dcalc = 1.257 g/cm3, Z = 8, sp. gr. Pbca. Molecule I adopts a strongly flattened boat conformation with the carbon atoms C-SO2Cl (C1) and C-i-Pr (C4) of the benzene ring deviating from the bottom of the boat by 0.065(1) and 0.032(1) A, respectively. Molecule I is sterically overcrowded, resulting in an increase in the bond lengths and bond-angle distortions in the fragment containing the SO2Cl group and two ortho-i-Pr groups. Nonbonded contacts that are present in the molecule can be considered weak intramolecular hydrogen bonds (for example, the (CH3)2C-H⋯O=S bond). There is no rotation of the SO2Cl, ortho-i-Pr, and CH3 groups. The above-mentioned facts are, apparently, responsible for the specific selectivity of TPSCl. New readily available sterically hindered arenesulfonyl chlorides were designed.