Subject tertiary prevention

Alkylation reactions are subject to the same constraints that affect all Sn2 reactions (Section 11.3). Thus, the leaving group X in the alkylating agent R—X can be chloride, bromide, iodide, or tosylate. The alkyl group R should be primary or methyl, and preferably should be allylic or benzylic. Secondary halides react poorly, and tertiary halides don t react at all because a competing E2 elimination of HX occurs instead. Vinylic and aryl halides are also unreactive because backside approach is sterically prevented. 

When one computes the amino acid substitution observed in protein of spontaneous or experimental TMV mutants, almost all the tryptic polypeptides clearly are subject to substitution except one—peptide IX. Changes in the tertiary structure of peptide IX are fatal to the protein configuration and prevent reaggregation of the RNA and virus protein. Uncoated RNA is rapidly digested by hydrolases. 

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