50  US 8,691,490 B2  49  In addition, the foregoing formula (L4-4) is to represent  one kind or a mixture of two or more kinds selected from  groups represented the following general formulae (L4-4-1)  to (L4-4-4 ).  As the acid-labile group of the foregoing formula (L4),  specifically the following groups are exemplified.  The foregoing general formulae (L4-1) to (L4-4 ), (L4-3- l ),  (L4-3-2), and (L4-4-1) to (L4-4-4) are to also represent all of  these enantiomers and a mixture of the enantiomers.  Meanwhile, a high reactivity in the acid-catalyzed elimi› nation reaction is realized when each of the bonding direc- tions of(L4-1) to (L4-4), (L4-3-l), (L4-3-2), and (L4-4-1) to  (L4-4-4) is to the exo-position of the bicyclo[2.2.1 ]heptane  ring (see Japanese Patent Laid-Open (kokai) No. 2000- 336121). In the preparation of a monomer containing a ter- tiary exo-alkyl group having these bicyclo[2.2.l]hepatane  skeletons as a substituent, there is a case to include a mono› mer that is substituted with an endo-alkyl group represented  by the following general formulae (L4-1-endo) to (L4-4- endo ). In such a case, to accomplish a good reactivity, the  exo-ratio is preferably 50% or more by mole, or more pref› erably 80% or more by mole.  In addition, as a tertiary alkyl group having 4 to 20 carbon  atoms, a trialkylsilyl group whose each alkyl group has 1 to 6  (IA-4-4)  (IA-4-3)  (IA-4-2)  (IA-4-1)  (IA-3-2)  (IA-3-1)  (L4-4-endo)  (L4-3-endo)  (L4-2-endo)  (L4-1-endo)  (See Japanese Patent Laid-Open (kokai) No. 2000- 336121.) 