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A compound that consists of only carbon and hydrogen, that contains at least one carbon-carbon double bond. Alkene names end with -ene . Examples are ethylene (CH 2 =CH 2 ); 1-propene (CH 2 =CH 2 CH 3 ), and 2-octane (CH 3 CH 2 =CH 2 (CH 2 ) 4 CH 3 ).