It has been presumed that the molten sulfur above $159^{\circ}C$ consists of an equilibrium mixture of $S_8$ rings and $S_x$ polymers where the number average degree of polymerization, P, is large. But it is known that admixture of halogens with liquid sulfur greatly reduce the viscosity. Constructing a new equilibrium equation, it is possible to evaluate the viscosity when halogens are added to liquid sulfur. Calculated viscosity is in good agreement with experimental values. Using the proposed model, the thermodynamic properties of liquid sulfur are also calculated over a wide range of temperature which the sulfur exists as the polymer.

Through-space and through-bonds interactions between two nonbonding orbitals are shown to be first-order and second-order perturbations of nonbonding orbitals by the framework sigma orbitals. Through-space interactions for diamines and triplet diradicals are always destabilizing, but through-bonds interactions are stabilizing owing to their coupling with through-space effect. Anomalies in level ordering and magnitudes of energy splitting can be rationalized with the present approach. Orbtial interactions predicted with the PMO method were found to be consistent with those obtained by STO-3G calculations and photoelectron spectroscopy.

The kinetic study on the bromine-exchange reaction of antimony tribromide with t-butyl bromide in nitrobenzene or 1,2,4-trichlorobenzene has been carried out, using Br-82 labelled antimony tribromide. The results show that the exchange reaction is first order with respect to t-butyl bromide and 1.5th order with respect to antimony tribromide. It is assumed that the 1.5th order indicates the coexistance of first- and second-order kinetics. Reaction mechanisms for the exchange reaction are proposed.

A new convenient method for the reduction of carboxylic acids to the corresponding alcohols via acyloxyborohydrides was explored. Acyloxyborohydrides, prepared from the reaction of various carboxylic acids and sodium borohydride, underwent reduction to the corresponding alcohols readily by the addition of dimethyl sulfate or Lewis acids, such as boron trifluoride etherate and triphenyl borate, presumably through acyloxyboranes. By utilizing this procedure, aliphatic and aromatic acids are rapidly and quantitatively reduced to the corresponding alcohols in terahydrofuran either at room temperature (or at $65^{\circ}$). This procedure provides selective reduction of carboxylic acids in the presence of halogen, nitro, and heterocyclic rings such as furan and thiophene.

$C_4$-Photocycloaddition of 8-methoxypsoralen (8-MOP) and 5,7-dimethoxycoumarin (DMC) to maleimide was studied in order to elucidate the mechanism of the photobiological activities of these molecules. The photoreaction was carried out in chloroform solution and frozen aqueous solution state. The major product was isolated and characterized by spectroscopic methods. The photoadduct between 8-MOP and maleimide was shown to be an 1:1 $C_4$-cycloadduct through the photocycloaddition of 4',5'-furyl double bond of 8-MOP to maleimide. The stereochemistry of cyclobutane ring of this photoadduct is consistent with the anti configuration. The photoadduct between DMC and maleimide was shown to be an 1:1 $C_4$-cycloadduct through the photocycloaddition of 3,4-pyrone double bond of DMC to maleimide.

9-Methylenethioxanthene(6) was synthesized and for the first time good mp and spectral data were taken. Reaction of (6) with thioxanthylium ion (1) in acetonitrile led to a carbenium addition adduct (8) which then was either attacked by a variety of nucleophiles subsequently added or underwent deprotonation reaction to give an olefin (13). From these reactions, was obtained bis-9,9'-thioxanthenylmethane (2). These results indicate clearly that (2) can be formed via (8) by accepting hydride. Isolation of (2) and (6) from the reaction of (1) with 9-methylthioxanthylium ion (18) also supports the involvement of (8) in the reaction of (1) with dimethylmercury. However, addition of thioxanthene radical (4) to (6) has not been ruled out.

The rate constants of the nucleophilic addition of thioglycolic acid to the derivatives $(H,\;p-CH_3,\;p-CH_3O,\;p-Cl,\;p-NO_2)$ of ${\beta}$-nitrostyrene were determined by ultraviolet spectrophotometry. The rate equations which can be applied over a wide pH range were obtained. Therefrom a reaction mechanism was proposed. Above pH 8.5 sulfide anion adds to the double bond (Michael type addtion). However, below pH 8.5, the neutral molecule and $HSCH_2COO^{\theta}$ add to the double bond.