is substituent group from alkyl group isobutyl group (CH3)2CH-CH2- -CH2-CH(CH3)2 0 2-methylpropan-1-ido 2-methylpropyl 57.070 57.11426 C4H9 CHEBI:30356 chebi_ontology iBu isobutyl leucine side-chain isobutane proteinogenic amino-acid side-chain group