 Those with two heteroatoms are more likely to occur as reactive intermediates.The C-X-C bond angles (where X is a heteroatom) in oxiranes and aziridines are very close to 60° and the peripheral H-C-H bond angles are near to 180°.The 5-membered ring compounds containing "two" heteroatoms, at least one of which is nitrogen, are collectively called the azoles.