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ORGANIC CHEMISTRY Once again the maximum bonds that can be made with carbon are four to satisfy octet. The bond angles between any two carbons in an alkane chain is 109.5, this is also true of methane. There exceptions of course, for example, cyclical structures have different bond angles. ALKYL Groups continued: Isopropyl – sec-butyl – iso-butyl – tert-butyl Nomenclature of Hydrocarbons Involving Halides Halides = Halogens = F, Cl, Br, I The nomenclature of naming hydrocarbons with Halides on them remains the same as naming a hydrocarbon containing an alkyl group. However, instead of Fluorine ethane it is Fluoroethane for example. Therefore change the -ine ending to –o for each halogen. What if there are two different halogens present on the same hydrocarbon? Then is there priority? No…just alpha order. But halogens get priority over alkyl groups. Cl Br Other examples: Draw the structure of mothballs: para-dichlorobenzene Aromatic Compounds are derivative of benzene Facts about Benzene First isolated by Michael Faraday, 1825 Colourless, sweetish-smelling liquid August Kekule proposed a ring structure with alternating single and double bonds. (1864) It is a planar molecule (flat) Studies show that the bond length are all the same: 139pm. (the bond length of C-C bond is 148pm while a C=C is 134pm) Naming benzene compounds: When benzene is represented as a branch that it is named: PHENYL When a benzene ring has substituents around it, then the normal method of naming a cyclical hydrocarbon is used. Numbering of the six carbon atoms is done such that the alkyl groups or other substituents have the lowest possible number. The two-Branches on a benzene deal: Chemists use a different method of naming benzene instead of using position numbers. The prefixes used are: ORTHO, META and PARA. ALCOHOL is coming up next …. No we are not going to drink!! Organic functional groups may bond with a carbon of an aliphatic compound to produce a compound with a new name but more importantly with physical and chemical properties that are unique to the functional group. ALCOHOL NOMENCLATURE Alcohols are compounds that contain the functional group –OH (Hydroxyl group). This hydroxyl group can be attached to one, or two or even three alkyl groups. The short way of representing an alkyl group is using R. Therefore: an alcohol can generally be represented at R-OH Recall: the presence of an OH group means that Hydrogen bonding is possible. Isomers are possible with alcohols containing more than 2 carbon atoms. What about priority of position numbers in a chain with different types of branch groups? Yes this is important. The priority is as follows: -OH > -F, -Cl, -Br, -I > -R groups Naming: 1. Find longest chain containing the –OH group and name the parent chain (look for double bonds etc for ending of hydrocarbon). 2. Change ending to –ol. For example CH3OH is named Methanol. If there is a double/triple bond involved then the Hydroxyl group gets priority. 3. If more than one hydroxyl group present then leave parent chain as it. Use prefix to represent number of OH present (di, tri, tetra etc) and add the –ol suffix. For example: CH3CH2OH C(CH3)3OH Draw the structures for the following: a) Ethylene glycol (1,2-ethanediol) b) 1-chloro-3,3-dimethyl-2-butanol Alcohols are classified according to the type of carbon atom bonded to the hydroxyl group: Primary Alcohol: RCH2-OH Secondary Alcohol: RR`CH-OH Tertiary Alcohol: RR`R”C-OH Note: R, R` and R” represents alkyl groups attached to carbon which in turn is bonded to the hydroxyl group. Aside: benzene attached to a single hydroxyl group is called a Phenol. Hmm…Why do I feel so sleepy? Do I smell an ether! ETHERS – The alkoxy alkane method Two hydrocarbons connected by an “O” (oxygen) and thus ether compounds have the formula R-O-R`. Mostly used for solvents in organic reactions Naming: 1. Larger R group is the parent chain. Name it as usual. 2. Smaller R group is the prefix but ending is alkOXY. 3. Write the alkoxy group followed by parent chain name. Examples: CH3CH2CH2OCH2CH3 CH3CH2CH2OCH(CH3)CH2CH3 So far we have considered single bonds between carbon and oxygen. Now, we will consider the naming of hydrocarbon compounds containing double bonds between carbon and oxygen (C=O). ALDEHYDES The aldehyde functional group can be represented by R-HC=O or R-CHO. This always appears at the end of a hydrocarbon chain. This makes the naming of an aldehyde simple. Naming: Remove the “e” ending of an alkane and replace with –al. Example: CH3CHO CH3CH2CHCH-CHO Draw the following: 4-bromo-3-methylheptanal and 3-hydroxybutanal.