CREATE TABLE table_2068719_1 (δs_ VARCHAR(255), _butadiene VARCHAR(255))
Name the number of δs ‡ /cal mol −1 k −1 for butadiene being 1,2-dimethylene-cyclohexane
    
SQL: SELECT COUNT(δs_) AS ‡__cal_mol_−1_k_−1 FROM table_2068719_1 WHERE _butadiene = "1,2-dimethylene-cyclohexane"