or c 6 alkyl the term u201c c 3 alkyl u201d as used herein means prop 1 yl and prop 2 yl isopropyl the term u201c c 4 alkyl u201d as used herein means but 1 yl but 2 yl 2 methylprop 1 yl and 2 methylprop 2 yl tert butyl the term u201c c 5 alkyl u201d as used herein means 2 2 dimethylprop 1 yl neo pentyl 2 methylbut 1 yl 2 methylbut 2 yl 3 methylbut 1 yl 3 methylbut 2 yl pent 1 yl pent 2 yl and pent 3 yl the term u201c c 6 alkyl u201d as used herein means 2 2 dimethylbut 1 yl 2 3 dimethylbut 1 yl 2 3 dimethylbut 2 yl 3 3 dimethylbut 1 yl 3 3 dimethylbut 2 yl 2 ethylbut 1 yl hex 1 yl hex 2 yl hex 3 yl 2 methylpent 1 yl 2 methylpent 2 yl 2 methylpent 3 yl 3 methylpent 1 yl 3 methylpent 2 yl 3 methylpent 3 yl 4 methylpent 1 yl and 4 methylpent 2 yl the term u201c crystalline u201d as used herein means having a regularly repeating arrangement of molecules or external face planes the term u201c substantial crystalline purity u201d as used herein means at least about 95 crystalline purity preferably about 97 crystalline purity.