Bonding between nonbonded sulfur and oxygen atoms in selected organic molecules (a quantum chemical study)

Abstract

A series of model compounds capable of intramolecular sulfur(II)-axygen interaction of the 1,5-type was investigated by the ab initio SCF-MO method. Compounds of the type X-S-A=B-Y(Z) =O with cis configuration about A=B, containing X = F, OH, NH2, CH,, and SH; A = CH; B = CH and N; and Z = H, 0, as well as lone pair, were studied. This resulted in four families containing a total of twenty compounds. The geometries of two basic planar conformations of these compounds, s-cis/s-trans (CT) and s-trans/s-trans (TT), obtained by internal rotations about the B-Y and S-C bonds, respectively, were optimized by using three different basis sets. These energy minimum conformations represent optimum geometries with and without S.-0 interactions, respectively. Four quantities were used to measure the extent of S.-0 interactions. These included the lengthening of the Y=O bond on going from TT to CT [AR(Y=O)], the shortening of the S.-O distance [AR(S-.O)], the energy change between TT and CT [ A E ( S -O ) ] , and the Mayer type bond order in the CT conformations [B(S-O)]. The linear interdependence of these four quantities indicated that each of these four parameters was about equally good measure of the extent of S-0 interaction. With the aid of these numerical measures earlier qualitative principles may now be evaluated quantitatively. Depending on the constitution of the individual compounds studied, the covalent character of the S.-O "bond" was found to be IO-30% of a usual single bond when sulfur d orbitals were included in the split-valence basis set. In compounds with X = OH, the O-S-.O moiety can be related to the nonequivalent 0-S-0 hypervalent bond of unsymmetrical sulfuranes.Intramolecular interactions between a pair of nonbonded fragments of a molecule have an important role in governing properties like conformation, spectroscopic behavior, or chemical reactivity. Moreover, after the pioneering work of Biirgi and Dunitz,' it has also been pointed out2 that the relative positions of reactive moieties in the crystalline state are in fact along the direction that one expects from reactants in the early stage of a given reaction. This of course offers an invaluable tool for the study of the initial part of a chemical reaction and yields important pieces of information about the reaction coordinate itself.An extremely interesting case, which is not yet fully understood, is the interaction of nonbonded S and 0 atoms, since these atoms do not escape from a very close contact. In fact a large number of organosulfur compounds are known, where the actual conformation is controlled by intramolecular sulfur-oxygen (S-0) interaction^.^*^ In these molecules the S-0 nonbonded distances are significantly shorter (2.03-3.00 A) than the sum of the corresponding van der Waals radii (3.25 A). The interest in these kinds of compounds is at least twofold. First, the stability of S-0 close contact conformations in c r y~t a l l i n e~~~ and gas4 phase may explain the unusual spectroscopic and physicochemical properties 'Permanent a...

2-Acylidene-3,5-diaryl-2,3-dihydro-1,3,4-thiadiazoles and related compounds: a question of hypervalent S … O interactions

“…The similar steric energies of both of the (Z) conformers is an additional argument for a hypervalent S.. .O interaction, whose energy need be no more than a few kilocalories to account for the overwhelming predominance of conformer 1. S.. .O interaction in CH,SCH=CHCHO to be equivalent to about 10% of a usual single bond (23).…”

Stereoelectronic properties of five anti-HSV-1 2′-deoxynucleosides analogues with heterocyclic substituents in the 5-position: A comparison with BVDU

“…The S˙˙˙O interaction between a pair of non-bonded fragments of a molecule are known and discussed (Lozac'h, 1971) but not yet fully understood. The quantum chemical interpretation of the nature of the S˙˙˙O interactions has to be attempted using the ab initio SCF-MO method (Angyan, 1987). The non-bonded SO interactions fall in the critical region between 2.0 and 3.0 Ǻ, which is not covered by any known type of S-O bonding.…”

“…The structure of 5-(5-chlorothien-2-yl)-2'-deoxyuridine (I) is part of a particular class of compounds characterized by a planar, conjugated five-membered "ring", closed by the non-bonded sulfur and oxygen atoms (Fig. 5) (Angyan, 1987). It seems that the S...O distances in the range 2.0-3.0 Ǻ are not accidental.…”

Nonbonded and interactions in 2-(4-chlorophenylthio) benzaldehyde in solution. An average skew conformation

“…-0 distances span 2.3-3.2 A , less than the sum of the van der Waals distances but greater than covalent bond lengths. Semi-quantitative interpretations of these phenomena have been given in terms of valence bond and molecular orbital models (2).…”