Least nuclear motion

It has also been called the antiperiplanar lone-pair hypothesis (ALPH). For a reinterpretation of this factor in terms of the principle of least nuclear motion (see 15-10), see Hosie,L. Marshall,P.J. Sinnott,M.L.y. Chem. Soc.,Perkin Trans. 2,1984,1121 Sinnott, M.L. Adv. Phys. Org. Chem., 1988, 24, 113. 

Lactam antibiotics, mechanisms of reactions, 23, 165 Least nuclear motion, principle of, 15, 1... 

Stereoelectronic control, the principle of least nuclear motion and the theory of, 24,113... 

Intermediates corresponding to the coordination step are considered as sufficiently close to transition states of the insertion reaction, and hence as suitable preinsertion intermediates, only if the insertion can occur through a motion of the nuclei that is near to the least—principle of least nuclear motion.13,30,31 For instance, for alkene polymerizations preinsertion intermediates correspond to geometries with (a) a double bond of the olefin nearly parallel to the metal growing chain bond and (b) the first C-C bond of the chain nearly perpendicular to the plane defined by the double bond of the monomer and by the metal atom (50° < Gi < 130°, rather than 0i 180° see below). 

Stability and reactivity of crown-ether complexes, 17, 279 Stereochemistry, static and dynamic, of alkyl and analogous groups, 25, 1 Stereoelectronic control, the principle of least nuclear motion and the theory of, 24, 113 Stereoselection in elementary steps of organic reactions, 6, 185 Steric isotope effects, experiments on the nature of, 10, 1... 

The Principle of Least Nuclear Motion and the Theory of Stereoelectric Control... 

According to the principle of least nuclear motion [45] aromatic deprotonation should be faster than benzylic metalation, because the benzylic carbanion is expected to rehybridize slightly toward sp2 to achieve stabilization by conjugation with the aromatic n system. This is, in fact, often observed [217, 401, 423-425], but with some substrates benzylic metalation can effectively compete with aromatic metalation[181, 425, 426] (Scheme 5.47). Thus, treatment of toluene with BuLi/TMEDA or BuLi/DABCO at 80 °C for 0.5 h or with BuLi/KOtBu in Et20 at -20 °C for 4 h leads to clean formation of benzyllithium [85, 427, 428], The kinetic preference for aromatic deprotonation, because of the principle of least nuclear motion, thus seems to be too weak to control the regioselectivity of deprotonations in all instances. 

Hine, J. The principle of least nuclear motion. Adv. Phys. Org. Chem. 1977, 15, 1-61. 

The frontier orbital explanation of the anomeric effect successes and failures 148 Calculations on tetrahedral intermediates 152 ALPH and the principle of least nuclear motion 154... 

In the third section, ALPH will be recast in terms of the principle of least nuclear motion, PLNM, which does not apply to reactions with late transition states. It will then be shown how for heterolytic reactions at saturated carbon, PLNM and ALPH make the same predictions. Key reactions of various compound types, which have been taken as evidence for ALPH, will be shown to be also predicted by PLNM. 

---