Mechanisms of thermal isomerization of allyl tetrazolyl ethers derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol were investigated. In the process of the syntheses of the three 1-aryl-5-allyloxytetrazoles, their rapid isomerization to the corresponding 1-aryl-4-allyltetrazol-5-ones occurred. The experiments showed that the imidates rearrange exclusively through a [3,3¢]-sigmatropic migration of the allylic system from O to N, with inversion. Mechanistic proposals are based on product analysis and extensive quantum chemical calculations at the DFT(B3LYP) and MP2 levels, on O-allyl and N-allyl isomers and on putative transition state structures for [1,3¢]-and [3,3¢]-sigmatropic migrations. The experimental observations could be only explained on the basis of the MP2/6-31G(d,p) calculations that favoured the [3,3¢]-sigmatropic migrations, yielding lower energies both for the transition states and for the final isomerization products.

a b s t r a c t 2-Allyl-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (ABIOD) has been studied by matrix-isolation infrared spectroscopy and quantum chemical calculations. A conformational search on the B3LYP/6-311++G(3df,3pd) potential energy surface of the molecule demonstrated the existence of three conformers, Sk, Sk 0 and C, with similar energies, differing in the orientation of the allyl group. The calculations predicted the Sk form as the most stable in the gaseous phase, whereas the Sk 0 and C conformers have calculated relative energies of ca. 0.6 and 0.8-3.0 kJ mol À1 , respectively (depending on the level of theory). In agreement with the relatively large (>6 kJ mol À1 ) calculated barriers for conformational interconversion, the three conformers could be efficiently trapped in an argon matrix at 10 K, the experimental infrared spectrum of the as-deposited matrix fitting well the simulated spectrum built from the calculated spectra for individual conformers scaled by their predicted populations at the temperature of the vapour of the compound prior to matrix deposition. Upon annealing the matrix at 24 K, however, both Sk and Sk 0 conformers were found to convert to the more polar C conformer, indicating that this latter form becomes the most stable ABIOD conformer in the argon matrix.

This work presents a new full dimensional potential energy surface for the ground singlet state of hydrogen peroxide, HO. This potential is based on a 3 × 3 matrix to accurately reproduce all the different dissociation channels in accordance with the Wigner-Witmer rules, namely, O(D) + HO(XA), OH(XΠ) + OH(XΠ), O(aΔ) + H(XΣ) e H(S) + HO(XA''). It has been obtained by fitting more than 38 thousand ab initio energies computed using the aug-cc-pVTZ and aug-cc-pVQZ basis sets and extrapolated to the basis set limit. The functional form used to represent the four-body short-range interactions is based on a sum of polynomial functions of the fourth degree multiplied by a range factor, both built with intrinsic permutation symmetry and centred at specific reference geometries, to which the ab initio points computed are assigned based on a k-means algorithm. It also accounts for the electrostatic dipole-dipole interaction between two OH(Π) fragments.