Chapter 3: Organic Compounds: Alkanes and Cycloalkanes

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1 hapter : rganic ompounds: Alkanes and ycloalkanes >11 million organic compounds which are classified into families according to structure and reactivity Functional Group (FG): group of atoms which are part of a large molecule that have characteristic chemical behavior. FG s behave similarly in every molecule they are part of. The chemistry of the organic molecule is defined by the function groups it contains 1

2 Alkanes arbon - arbon Multiple Bonds arbon-heteroatom single bonds basic X N Alkenes X= F, l, Br, I Alkyl alide amines Alkynes alcohols acidic ethers thiols S S sulfides (disulfides) Arenes arbonyl-oxygen double bonds (carbonyls) arbon-nitrogen multiple bonds aldehyde carboxylic acid acidic l acid chloride N imine (Schiff base) basic ketones ester anhydrides N nitrile (cyano group) N amide opsin Lys-N 2 rhodopsin + Lys- opsin N 2

3 Alkanes and Alkane Isomers Alkanes: organic compounds with only - and - single (s) bonds. general formula for alkanes: n (2n+2) Saturated hydrocarbons ydrocarbons: contains only carbon and hydrogen Saturated" contains only single bonds Isomers: compounds with the same chemical formula, but different arrangement of atoms onstitutional isomer: have different connectivities (not limited to alkanes) butanol diethyl ether straight-chain or normal hydrocarbons branched hydrocarbons n-butane n-pentane Systematic Nomenclature (IUPA System) Prefix--Suffix - number of carbons Prefix- substituents Suffix- functional groups

4 Naming Alkanes General Formula: n (2n+2) suffix: -ane Names: 1 4 Methane 4 2 Ethane Propane 8 4 ( 2 ) 2 Butane 4 10 ( 2 ) Pentane 12 6 ( 2 ) 4 exane ( 2 ) eptane ( 2 ) 6 ctane ( 2 ) 7 Nonane ( 2 ) 8 Decane Alkyl substituents (group): carbon chains which are a substructue of a molecule one carbon group off a main chain R= Rest of the molecule (mainchain) 1 -R Methyl 2 2 -R Ethyl 2 2 -R Propyl 4 ( 2 ) 2 2 -R Butyl ( 2 ) 2 -R Pentyl 6 ( 2 ) 4 2 -R exyl 7 ( 2 ) 2 -R eptyl 8 ( 2 ) 6 2 -R ctyl 9 ( 2 ) 7 2 -R Nonyl 10 ( 2 ) 8 2 -R Decyl 4

5 Rules for Systematic Nomenclature of Alkanes 1. Find the parent chain a. Identify the longest continuous carbon chain as the parent chain carbons = hept- 2 2 b. If more than one different chains are of equal length (number of carbons), choose the one with the greater number of branch points (substituents) as the parent branch pts. 1 branch pt. 2. Numbering the carbons of the parent chain a. Number the carbon atoms of the parent chain so that any branch points have the lowest possible number branch pts. at carbons and 4 branch pts. at carbons 4 and b. If there is branching equidistant from both ends of the parent chain, number so the second branch point has the lowest number branch pts. at carbons, 6, 7 branch pts. at carbons,4,7

6 . Substituents a. Identify and number the substituents and list them in alphabetical order ethyl -9 = nonane methyl 7-methyl 4,7-dimethyl b. If there are two substituents on the same carbon, assign them the same number. 4. Write out the name a. Write out the name as a single word: hyphens (-) separate prefixes commas (,) separate numbers b. Substituents are listed in alphabetical order 4c. If two or more identical substituents are present use the prefixes: di- for two tri- for three tetra- for four note: these prefixes (di-, tri-, tetra-, etc.) are not used for alphabetizing purposes ethyl-4,7-dimethylnonane

7 . omplex Substituents (substituents with branching) a. Named by applying the four previous rules with some modification b. Number the complex substituent separately from the parent. Begin numbering at the point of attachment to the parent chain. c. omplex substituents are set off by parenthesis ,6-dimethyl-4-(1-methylpropyl)decane Nonsystematic (trivial) Names: -carbons: 4-arbons: - arbons: hain Isopropyl- (1-methylethyl) 2 hain sec-butyl- (1-methylpropyl) 2 2 hain Isopentyl-, isoamyl (-methylbutyl) Isobutyl- (2-methylpropyl) Alphabetizing trivial names: Iso- and neo are part of the alkyl group name and are used for alphabetizing. sec- and tert- are not included in the alphabetical order. 2 hain 2 hain neopentyl- (2,2-dimethylpropyl) hain tert-butyl- (1,1-dimethylethyl) 2 hain tert-pentyl-, tert-amyl (1,1-dimethylpropyl) 4-(1-methylethyl)heptane -or- 4-Isopropylheptane 2-methyl-6-(2-methylpropyl)decane -or- 6-Isobutyl-2-methyldecane 7

8 Degrees of Substitution Primary (1 ) arbon: carbon which is bonded to only one other carbon Secondary (2 ) arbon: carbon which is bonded to two other carbons Tertiary ( ) arbon: carbon which is bonded to three other carbons Quarternary (4 ) arbon: carbon whohc is bonded to four other carbons secondary alcohol Primary (1 ˇ) Secondary (2 ˇ) Tertiary ( ˇ) Quarternary (4 ˇ) 1 ydrogens- hydrogens on a primary carbon. - (methyl group) 2 ydrogens- hydrogens on a secondary carbon (methylene group) ydrogens- hydrogens on a tertiary carbon. (methane group) 2 2 methyl group: 1 hydrogens methylene group: 2 hydrogens methine group: hydrogens Applied to other functional groups: n-butanol 1 alcohols 2 sec-butanol 2 alcohol tert-butanol alcohol 8

9 Alkanes show: regular increase in bp and mp as the molecular weight increase. Branching lowers the bp or alkanes n-pentane bp= 6.1 i-penatane bp= 27.9 neo-pentane bp= 9. Van der Waals Forces: small temporary dipoles that are a result of a Distortion of the electron clouds. There is an attraction between molecules as result of these temporary dipoles ycloalkanes hain hain Propane yclopropane cyclopropyl eptane ycloheptane ycloheptyl Butane yclobutane yclobutyl hain hain hain ctane yclooctane yclooctyl Pentane yclopentane yclopentyl hain hain Nonane yclononane yclononyl exane yclohexane yclohexyl hain Decane yclodecane yclodecyl 9

10 Naming ycloalkanes General Formula: n (2n) 1. hain a. Use the cycloalkane as the parent chain if it has a greater number of carbons than any alkyl substituent. b. If an alkyl chain off the cycloalkane has a greater number of carbons, then use the alkyl chain as the parent and the cycloalkane as a cycloalkyl- substituent. Methylcyclopentane 2-yclopropylbutane 2. Numbering the ycloalkane a. When numbering the carbons of a cycloalkane, start with a substituted carbon so that the substituted carbons have the lowest numbers (sum) ,-Dimethylcyclohexane not- 1,-Dimethylcyclohexane ,2,4-Trimethylcyclohexane ( = 7) -not- 1,,4-Trimethylcyclohexane ( = 8) 2. b. When two or more different substituents are present, number according to alphabetical order Ethyl-2-methylcyclohexane 2 -not- 2-Ethyl-1-methylcyclohexane. alogen Substituents alogen substituents are treated exactly like alkyl groups: -F fluoro- -l chloro- -Br bromo- -I iodo- 1-hloro-2-methylcyclobutane l 10

11 2 2 chrysanthemic acid grandisol prostaglandin E 1 esterone testosterone 11