烃 is a chemistry-coined character:
火 (fire) radical for combustibles +
巠/
圣 phonetic. The word reflects its composition —
碳 (tàn, carbon) +
氢 (qīng, hydrogen) →
烃 (tīng), with the pronunciation borrowing from the second character's onset. Compounds:
烷 wán (alkane),
烯 xī (alkene),
炔 quē (alkyne) all use the
火 radical for the same reason.
