Molecular strain energy

The ring-opening polymerization reactions depend upon thermodynamic and kinetic factors, and on the total molecular strain energies of the particular ring structures. Six-membered -valero-lactam is the most stable ring structure and most difficult to polymerize. Also, the presence of substituents increases the stability of the rings and decreases the ability to polymerize. 

Fig. 10. The acyclic quasilinear conformer of lasalocid anion which predominates under high polarity conditions. This conformer has the lowest intrinsic molecular strain energy as calculated using a QCFF energy minimization program - . Solvent effects on the conformation were modeled using an empirical specific site approach ...

The compact cage molecules, octanitrocubane and tetranitro tetraazacubane and diazadinitro tetrahedrane, have molecular strain energy locked-in which is released along with the internal combustion energy when they explode. The strain energies in these molecules are high as demonstrated in Table 4 for the case of cubane. 

PC Model has some features that are not found in many other molecular mechanics programs. This is one of the few programs that outputs the energy given by the force field and the heat of formation and a strain energy. Atom types for describing transition structures in the MMX force field are included. There is a metal coordination option for setting up calculations with metal atoms. There are also molecular similarity and conformation search functions. 

Once requiring minicomputers and worksta tions many molecular mechanics programs are avail able for personal computers The information that strain energy calculations can provide is so helpful... 

Make molecular models of c/s and trans 1 2 dimethylcy clopropane and compare their strain energies... 

Mesitylene (13 5 trimethylbenzene) is the most stable of the tnmethylbenzene isomers Why2 Which isomer do you think is the least stable" Make a molecular model of each isomer and compare their calculated strain energies with your predictions Do space filling models support your explanation" ... 

Make molecular models of the two chair conformations of cis 1 tert butyl 4 phenyl cyclohexane What is the strain energy calculated for each conformation by molecular mechanics Which has a greater preference for the equatorial onentation phenyl or tert butyD... 

The distorted structure can be replaced by a more reasonable structure using an empir ical molecular mechanics calculation This calculation which is invoked m Spartan Build by clicking on Minimize, automatically finds the structure with the smallest strain energy (m this case a structure with realistic bond distances and a boat conformation for the SIX membered ring)... 

Molecular mechanics strain energies have another use They can also be used to com pare the energies of models that share the same molecular formula that is models that are either stereoisomers or different conformations of a single molecule (allowed com parisons are shown here)... 

Alkenes exhibit large strain energy when molecular geometry does not permit all the bonds to the two sp -hybridized carbons to be coplanar. An example that illustrates this point is -cycloheptene ... 

Cyclobutanc, angle strain in. 115-116 conformation of. 115-116 molecular model of, 116 photochemical synthesis of, 1190 strain energy of, 114 torsional strain in, 115-116 Cyclodecane, strain energy of. 114 Cyclodecapentaene, molecular model of, 525, 540... 

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