Orientational bias

The normalized Rosenbluth factor of the isolated chain has to determined from a separate (but very fast) simulation. A related technique, the orientational-bias insertion [2,39,40] is suitable for fluids where part of the interactions is strongly orientation-dependent. 

Lithium enolates exist as large aggregates and their approach to the electrophile is restricted by steric and electronic considerations, as well as by the relative geometry of the molecule. Despite the structural complexity remarkably good predictions for reactivity and diastereoselectivity can be made based on the steric requirements that would be present in a monomeric system. For example, in most reactions of enolate anions the electrophile will be delivered to the less hindered face of the enolate to give the major product. In all models used to describe reactivity (secs. 9.5.A.iii-9.5.A.v), a monomeric enolate will be shown but the facial and orientational bias of the enolate is clearly influenced by the state of aggregation in solution. 

Enolates derived from cyclic compounds such as cyclohexane carboxylic acid or cyclohexane carboxalde-hyde generate enolates that are unique. These enolates have an exocyclic double bond that can exist as ( ) and (Z) isomers. The facial and orientational bias in alkylation and condensation reactions of such enolates is influenced by the conformation of the ring it is attached to. Alkylidene cyclohexane enolates show a preference for equatorial attack, just as cyclohexanone derivatives do (sec. 4.7.C,D). 

MCY water, Grand canonical (ixVT) MC/MD, orientational-bias MC... 

Orientational bias moves are useful for the study of fluids that exhibit highly directional forces. A prime example of such a fluid is water, where strong hydrogen bonding interactions lead to well defined, relatively stable low-energy molecular structures. Cracknell et al. [3] were among the first to use orientational bias for the study of water. A typical orientational bias... 

Bulk water has been the subject of a large number of simulation studies. Water in confined environments has been studied less extensively and, more importantly to the goals of this chapter, it represents a case where orientational bias moves are particularly helpful. 

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