The electronic properties of poly(diacetylenes) were investigated by Using the valence effective Hamiltonian (VEH) method. The molecular geometries considered were appropriately optimized. The relative effects of the polymer backbone geometry, the presence of conformational defects along the polymer chain backbone, the chemical/electronic nature of the substituents, and the conformation of the side groups upon the electronic structure were investigated.

A mMOkUkabitplCdCUhOM ' (MnroO/3) using energy minimized mokcuh geomehies w m performed 011 oxidimd and reduced luminavin and related methylared isopllouzina. including cationic and anionic unpatvw of opimitcd geomu&s for thtse mokcular systems and provides the basis f a intcrpntation of but also highly fkxibk .bau thc N(5)-N(10) axis; only I kd/mol is requid for a 10" bend. N(10) is tuted irollbxuiac is comprtcd to k 0.76 Lul/mol (AH) lcss stable than its isomcr, OlloxrZine. Calcula-R c d d flntin BeDmctry depends 011 methyl rubstitutioa putern: N( 10) substituted fomu arc b a t with typicrl fold angles d 15Y, w h m u the unsubstitutcd reduced form is planar. Both oxidized and reduced form ale aim fkxible.Proton clffinitier wuc ulcui.ted for protonuion and deprotonatlon of oxidized and raluccd forms. Protoruth of oxidized fams is favored at N( I ) by 10-12 kal/mol and products somwhat nonplanar isoalloxuinium ions. In addition, AH for the two-electron reduction of lumiflrvin is estimated to be -19.7 L#l/mol.In this p~p r investigations of geomcaiC aspects an presented along with introductory and background mrtcrirl. Orbital ~mrmrr and ekctron diotribution srudi an prrscntcd in paper 11. spccics. ckrcapanalt withexperimcntpl geomeay, phototlazroa spectra. and Nkllt drcrsupports the chanicrl md bioio&d plopnic* oxidized famr ale shown to be most stable in h e p I . M I c O n f 1~ gawnlly OUI of thc plme slightly; aim, C(9)-methyl substiattion introduas fhmphxity. The uasubstitioar ~a l s o p r f o r n w d o o d as well asquinonc-mcthkle tautomenc . forms.

A b s b r tBued oa MINW/J optimized gcolaetnes '

No abstract

Polymer conformational analyses can require being able to model the intramolecular energetics of a very long (infinite) chain employing calculations carried out on a relatively short cham sequence. A method to meet this need, based upon symmetry considerations and molecular mechanics energetics, has been developed. Given N equivalent degrees of freedom in a linear polymer chain, N unique molecular groups are determined within the chain. A molecular unit is defined as a group of atoms containing backbone rotational degrees of conformational freedom on each of its ends. The interaction of these N molecular groups, each with a finite number of nearest neighbors, properly describe the intramolecular energetics of a long (infinite) polymer chain. Thus, conformational energetics arising from arbitrarily distant neighbor interactions can be included in the estimation of statistical and thermodynamic properties of a linear polymeric system. This approach is called the polymer reduced interaction matrix method (PRIMM) and the results of applying it to isotactic polystyrene (I-PS) are presented by way of example.