Functional Group : An atom or group of atoms, bound together chemically, that has an unpaired electron, which when it attaches itself to the hydrocarbon backbone, imparts special properties to the new compound thus formed
Tatyana Davletshina, Industrial Fire Safety Guidebook, Noyes Publications, New Jersey 07675, USA 1998. http://www.aura-o.aura-astronomy.org/aura/sites/de fault/files/files/Referencia_Bibliografica/industr ial%20fire%20protection%20handbook.pdf, (IndFrS - Amer) {470}