The longest official word ever (1,913 letters) is the term for the formula C₁₂₈₉H₂₀₅₁N₃₄₃O₃₇₅S₈

Methionylglutaminylarginyltyrosylglutamylserylleucylphenyl-
alanylalanylglutaminylleucyllysylglutamylarginyllysyglutamyl-
gycylalanylphenylalanylvalylprolylphenylalanylvalylthreonyl-
leucylglycylaspartylprolylglycyllisoleucylglutamylglutaminyl-
serylleucyllysylisoleucylaspartylthreonylleucylisoleucyl-
glutamylalanylglycylalanylaspartylalanylleucylglutamylleucyl-
glycylisoleucylprolylphenylalanylserylaspartylprolylleucyl-
alanylaspartylglycylprolylthreonylisoleucylglutaminylasparaginyl-
alanylthreonylleucylarginylalanylphenylalanylalanylalanyl-
glycylvalylthreonylprolylalanylglutaminylcysteinylphenylalanyl-
glutamylmethionylleucylalanylleucylisoleucylarginylglutaminyl-
lysylhistidylprolylthreonylisoleucylprolylisoleucylglycylleucyl-
leucylmethionyltyrosylalanylasparaginylleucylvalylphenylalanyl-
asparaginyllysylglycylisoleucylaspartylglutamylphenylalanyl-
tyrosylalanylglutaminylcysteinylglutamyllysylvalylglycylvalyl-
aspartylsrylvalylleucylvalylalanylaspartylvalylprolylvalyl-
glutaminylglutamylserylalanylprolylphenylalanylarginylglutaminyl-
alanylalanylleucylarginylhistidylasparaginylvalylalanyl-
prolylisoleucylphenylalanylisoleucylcysteinylprolylprolylaspartyl-
alanylaspartylaspartylaspartylleucylleucylarginylglutaminyl-
isoleucylalanylseryltyrosylglycylarginylglycyltyrosylthreonyl-
tyrosylleucylleucylserylarginylalanylglycylvalylthreonylglycyl-
alanylglutamylasparaginylarginylalanylalanylleucylleucyllysyl-
glutamyltyrosylasparaginylalanylalanylprolylprolylleucylglutaminyl-
glycylphenylalanylglysylisoleucylserylalanylprolylaspartylglutaminyl-
valyllysylalanylalanylisoleucylaspartylalanylglycylalanylalanyl-
glycylalanylisoleucylserylglycylserylalanylisoleucylvalyllysylisoleucyl-
isoleucylglutamylglutaminylhistidylasparaginylisoleucylglutamyl-
prolylglutamyllysylmethionylleucylalanylalanylleucyllysylvalylphenyl-
alanylvalylglutaminylprolylmethionyllysylalanylalanylthreonylarginy-
lserine.