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Unformatted text preview: Chapter 2 The Nature of Organic Molecules 2.1 Functional Groups 1. Functional group is a group of atom within a larger molecule that has a characteristic chemical behaviour. Functional groups make it possible to classify compounds by reactivity. 2. a given function group behaves almost the same way in any molecule its in. This is because the electronic structure of the functional group remains essentially the same in all molecules it occurs, its reactivity remains the same 3. For example, alkene reacts with Br 2 to give products in which a bromine atom is added to each of the double bonded carbon and the double bond is changed to single bond in the product. 4. The chemistry of every organic molecule, regardless of the size and complexity, is determined by the function groups it contains 5. See page 35 fig 2.1 for reaction between alkene and Br 2 Functional Groups with Carbon-Carbon Multiple Bonds 1. Includes Alkene, Alkyne and Arene. 2. Alkenes have at least one double bond between C-C, alkynes have at least one triple bond between C-C. Arenes have alternating double and single bond in a six-membered ring of carbon atoms. The cycle of bonds in arene leads to different reactivity. Functional Groups with Carbon Singly Bonded to Electronegative Atom 1. Alkyl Halides, alcohol, ethers, amines, thiols and sulfides all have carbon atom singly bonded to an electronegative atom Nitrogen, halogen, oxygen or sulphur. 2. Alkyl Halides have a carbon atom bonded to halogens (-X) Alcohols have a carbon atom bonded to OH group ethers have two carbon atoms bonded to the same Oxygen (-O-) amines have a carbon atom bonded to NH 2 thiols have a carbon atom bonded to SH group sulfides have two carbon atoms bonded to the same sulphur (-S-) 3. in all cases, the bonds are polar with the carbon atom bearing a partial positive charge ( + ) and the electronegative atom bearing a partial negative charge ( - ) . Functional Groups with Carbon-Oxygen Double Bond (Carbonyl Groups) 1. Carbonyl group C=O is common to many families of compounds and are present in some of the most important compounds in organic chemistry. 2. The chemistry of these compounds ( ones containing carbonyl group, C=O) depends greatly on the identity of atoms bonded to the carbonyl group carbon, (C*=O). 3. Thus, Carbonyl group gives rise to many different classes of functional groups depending on the atoms bonded to the carbonyl group carbon. 4. Aldehydes have at least one hydrogen bonded to C=O ( the carbonyl group carbon is bonded to one hydrogen and one C of the chain), -CHO. Ketones have two carbons bonded to C=O (-CO- ) Carboxylic acids have one carbon and one OH group bonded to C=O group (-COOH) esters have one carbon and one ether like oxygen bonded to C=O ( -COO) Ami d es have one carbon and one N bonded to the C=O (-CONH) Acid chlorides have one carbon and one chlorine bonded to the C=O(- COCl) ....
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