Branched-chain alkanes are preferred as they are much less prone to premature ignition, which causes knocking, than their straight-chain homologues.
bɹˈæntʃttʃˈeɪn ˈælkeɪnz ɑːɹ pɹɪfˈɜːd æz ðeɪ ɑːɹ mˈʌtʃ lˈɛs pɹˈoʊn tə pɹɪmətʃˈʊɹ ɪɡnˈɪʃən, wˌɪtʃ kˈɔːzᵻz nˈɑːkɪŋ, ðɐn ðɛɹ stɹˈeɪttʃˈeɪn hˈɑːməlˌɑːɡz.