Strain energy of three-membered rings: a new ultradiagonal definition as applied to silicon- and carbon-containing species

The strain energy of perchlorocyclopropane is small: It might even be negative. A density functional theory study of perhalocycloalkanes

“…The final approach discussed here makes use of diagonal 17 and ultradiagonal 18 reference species, 1/6(C 6 X 12 ) and 1/2(C 6 X 12 ), with which the SE is defined as and, in this case, numerically identical to For the parent, perfluorinated, and perchlorinated cyclopropanes within this model, the calculated SEs are 25.2, 45.6, and −12.1 kcal/mol, respectively. Using experimentally measured enthalpies of formation, the SE of cyclopropane is 27.5 kcal/mol.…”

Small heterocyclics as hydrogen bond acceptors and donors: the case of the C2H3XS···NH3 complexes (X = H, F and CH3)

“…In organic chemistry, it is known that there are an enormous variety of nucleophilic mechanisms [1], and that, in these, the heterocyclic compounds are important intermediaries owing to their high reaction capacity [2], which is essentially a function of the strained ring energy [3]. Thiirane (C 2 H 4 S), in particular, is a three-member heteroring possessing properties internally related to nucleophilic reaction mechanisms [4].…”

“…Thiirane (C 2 H 4 S), in particular, is a three-member heteroring possessing properties internally related to nucleophilic reaction mechanisms [4]. In order to understand the functionality of C 2 H 4 S in nucleophilic reactions, one of the most widely used courses of investigation is the characterization of transition state based on interaction between C 2 H 4 S and a number of well-known nucleophiles [5], such as ammonia (NH 3 ). According to Banks [6], elucidation of the reactivity of thiirane with ammonia has been reported, according to which structures of the transition state have been examined through the application of sophisticated computational methods.…”

“…According to Banks [6], elucidation of the reactivity of thiirane with ammonia has been reported, according to which structures of the transition state have been examined through the application of sophisticated computational methods. It is therefore argued that NH 3 interacts with thiirane specifically on carbons of its CH 2 methyl groups undergoing a SN 2 generalized reaction mechanism. Nevertheless, it is also known that small compounds such as C 2 H 4 S and similar heterorings have been widely studied with regard to hydrogen-bonded complexes [7,8].…”

“…However, except in cases reported by Banks and White [10], it should be stressed that in terms of intermolecular parameters, such as those routinely used for studying hydrogen-bonded complexes, no study of the interaction of nucleophiles such as NH 3 until now. It is naturally assumed that hydrogen bonding criteria can be used to investigate nucleophilic interactions of NH 3 with C 2 H 4 S. In other words, it is conceivable that the C 2 H 4 SÁÁÁNH 3 hydrogen-bonded complex is formed.…”