Kosower

Kosower E M and Huppert D 1983 Solvent motion controls the rate of intramolecular electron transfer Chem. Phys. Lett. 96 433-5... 

J-Tosyloxy. d -steroids, e.g. O-tosylcholesterol, give 3,5-cyclosteroids (— /-steroids) on addition of nucleophiles. Internal hydroxyl displacement, e.g. with PClj, leads to 3fi-substituted products or overall retention of configuration at C-3 by rearrangement of the 6/5 substituent (E.M. Kosower, 1956). 

Submitted by Lester Friedman and Edward Kosower. Checked by Reynold C. Fuson and Elliott N. Marvell. 

It has been purified by distilling from K2CO3 under high vac and fractionated in an all-glass apparatus. The middle fraction is collected, degassed (seven or eight freeze-thaw cycles) and redistd under as high a vacuum as possible [Mohammad and Kosower J Am Chem Soc 93 2713 1971]. 

Nitrobenzyl alcohol [619-73-8] M 153.1, m 93 . Crystd from EtOH and sublimed in a vacuum. Purity should be at least 99.5%. Sublimed samples should be stored in the dark over anhydrous CaSOa (Drierite). It the IR contains OH bands then the sample should be resublimed before use. [Mohammed and Kosower J Am Chem Soc 93 2709 1979.]... 

Lithium perchlorate [7791-03-9] M 106.4, pK -2.4 to -3.1 (for HCIO4). Crystd from water or 50% aq MeOH. Rendered anhydrous by heating the trihydrate at 170-180° in an air oven. It can then be recrystd twice from acetonitrile and again dried under vacuum [Mohammad and Kosower J Am Chem Soc 93 2713 19711... 

Kosower, E.M. An Introduction to Physical Grganic Chemistry Wiley New York, 1968. 

Kosower made the first use of this phenomenon for measuring solvent polarity. The model process is the absorption transition of l-ethyl-4-carbomethoxy-pyridinium iodide, 7 ... 

Figure 8-7. Model of the alkylpyridinium iodide complex (4) ground state. (B) Excited state [after Kosower ]...

A proposed explanation of the reactivity of the 4-position versus that of the 2-position in pyridinium compounds has been advanced by Kosower and Klinedinst nucleophiles which are expected to form charge-transfer complexes will tend to substitute at the 4-position. However, it is not clear why this (usually unknown) property should govern the site of substitution, except for a bifunctional nucleophile such as hydrosulfite ion which can form a suitable bridge from the nitrogen to the 4-position. 

E. M. Kosower, in An Introduction to Physical Organic Chemistry", Wiley, New York (1962). 

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