Chemistry

15 Organic Compounds107Quick Quiz1. What are allotropes?2. Why it was given the name Bucky balls?15.6 FUNCTIONAL GROUPS AND HOMOLOGOUS SERIES15.6.1 Functional GroupThe basic idea of the functional group is at the heart of much of the organic chemistry weshall study. We will carry out many transformations of organic molecules. In most cases thechange will occur at one “spot” in the original reacting molecule. That spot is the functional group.A functional group is anatom or group of atoms in amolecule that gives the moleculeits characteristic chemicalproperties. Double and triplebonds are functional groups. Otherexamples include -Cl, -Br, -OH,-NH2 groups. Remember that thefunctional group is the action group.The hydrocarbon portion remainsinert.Fig. 15.2We often use the symbol R- torepresent the hydrocarbon portion to which the functional group is attached. Thus R- can CH3- ,CH3CH2-, (CH3)2CH- or any other group of C and H atoms with one free valence by which thefunctional group is attached. The table 15.1 shows some common functional groups and thecorresponding classes of compounds.Each functional group undergoes characteristic reactions. By recognizing the functionalgroup in a molecule, it is possible to predict the reactions which that molecule will undergo. Theconcept of functional group is important to organic chemistry for three reasons:1) Functional groups serve as basis for nomenclature (naming) of organic compounds.2) Functional groups serve to classify organic compounds into classes/families. All compoundswith the same functional group belong to the same class.3) A functional group is a site of chemical reactivity in a molecule containing the functionalgroup.A molecule can contains more than one functional group. It is then said to bePolyfunctional, and the properties of each functional group may be modified by the presenceof the others.