Nucleophilic identity substitution reactions. The reaction between ammonia and protonated amines

The gas phase reactions between NH3 and the protonated amines MeNH3+, EtNH3+, PriNH3+, and Bu(t)nH3+ have been studied by high level ab initio methods. Mass spectrometric experiments yielded no significant reaction products; this result being consistent with the calculated reaction barriers. The potential energy profiles for both nucleophilic substitution (SN2) and elimination (E2) pathways have been investigated. Both back side Walden inversion (SNB) and front side (SNF) nucleophilic reaction profiles have been generated. The SNB reaction barriers are found to be higher for the more alkyl substituted reaction centres. Reaction barrier trends have been analysed and compared with the results of a similar study of the H2O-ROH2+ system (R = Me, Et, Pri, and Bu(t)).     

Synthesis of long-chain fatty acid enol esters isolated from an environmental DNA clone

[structure: see text] Long-chain fatty acid enol ester 1 is the major metabolite of a new family of small molecules isolated from the heterologous expression of environmentally derived DNA. A versatile synthesis of 1, in which an aromatic acetaldehyde is O-acylated with a long-chain acyl chloride allowed for the rapid construction of both the isolated product (1) and a number of structural analogues (including 8, 17, and 18).     

Synthesis of 2,4-methanoproline

An efficient synthesis of 2,4-methanoproline from serine is described. The cyclobutane is formed by a sensitized intramolecular [2+2] photoaddition.     

The cyanomethyl group for nitrogen protection and iminium ion generation in ring-enlarging pyrrolidine annulations. A short synthesis of the amaryllidaceae alkaloid d,1-crinine

The preparation of $\text{cis}$-3a-aryl-4-oxo-decahydrocyclohepta[b]pyrroles and $\text{cis}$-3a-aryl-4-oxo-octahydroindoles is facilitated by using a cyanomethyl group to both protect nitrogen and serve as a precursor for a formaldehyde iminium ion.     

Classical chemical concepts from ab initio SCF calculations

Alternative definitions of bond order, valency, gross orbital populations and total atomic charge for SCF wavefunctions are compared. It is found that there are sound theoretical and numerical reasons for preferring definitions based on the Löwdin density matrix.     

Geometry and conformation of dimethyl sulphate as investigated by electron diffraction and dipolometry

Electron diffraction data of dimethyl sulphate are interpreted by a 2:1 mixture of the C₂ and C_2v rotamers. This finding is also in agreement with the dipole moments of dimethyl sulphate and diethyl sulphate in benzene solution. The SO bond length and OSO bond angle are in agreement with the previously described empirical relationships. The variations in the O ?O distances in the different moieties OSO , OS-O, O-S-O, deserve special attention.