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Organic Nomenclature: Naming Organic Molecules Aerated Alkali What’s in a name? Mild Vegeta ble Alkali Tartarin Glauber's Alka hest t o lm e H n a V f o t s e Alkah Fixed Vegetable Alkali R ussian Pot Ash es e l l e v a r G s e Cendr lkali A e l b a t r e g e Mild V ta r a T f o K2CO3 li a k Al Sal Juniperi Alkahest of Reapour Potassium Carbonate Salt of Tachenius Sal Ta Salt o rtari dA xe Sal Gentia nae Reguline Caustic sh A d Woo Fi Alkali of Wine Lees German Ash Oil of Tartar Pearl Ash alt li S lka f Wor o n g mwo Li i t a l x l e e v od a i l c C s a e i r e a n i u C Sal Alkanus Vegetablis Sal G IUPAC Rules for naming organic molecules International Union of Pure and Applied Chemists 3 Name Alkanes CnH2n+2 Prefix Methane Molecular Formula CH4 Ethane C2H6 Eth Propane C3H8 Prop Butane C4H10 But Pentane C5H12 Pent Hexane C6H14 Hex Heptane C7H16 Hept Octane C8H18 Oct Nonane C9H20 Non Decane C10H22 Dec Meth 4 Structure of linear alkanes propane butane heptane nonane pentane hexane octane decane 5 Constitutional Isomers: molecules with same molecular formula but differ in the way in which the atoms are connected to each other 6 Physical properties of constiutional isomers 7 Isomers The more carbons in a molecule, the more possible ways to put them together. n 1 2 3 4 5 6 7 8 9 10 15 25 # of isomers 1 1 1 2 3 5 9 18 35 75 4,347 36,797,588 8 Naming more complex molecules hexane C6H14 9 Naming more complex molecules Step 1: identify the longest continuous linear chain: this will be the root name: this is the root name 2 1 1 4 6 3 2 longest chain = 6 (hexane) 5 2 4 3 5 2 4 1 longest chain = 5 (pentane) 1 3 3 5 correct longest chain = 5 (pentane) 1 4 longest chain = 4 (butane) 2 2 3 1 3 4 incorrect 4 longest chain = 4 (butane) 10 Naming more complex molecules Step 2: identify all functional group (the groups not part of the “main chain”) CH3 2 1 2 4 3 5 main chain: pentane 4 3 1 5 CH3 main chain: pentane CH3 1 2 3 1 4 CH3 CH3 main chain: butane 2 3 4 CH3 main chain: butane 11 Alkyl groups: fragments of alkanes H H C H H H C H H methane methyl CH4 CH3 empty space (point where it attaches to something else) 12 More generally... H H H C C H H ethyl C2H5 H H H H C C C H H H propyl C3H7 CnH2n+1 H H H H H C C C C H H H H butyl C4H9 13 Naming more complex molecules CH3 2 1 2 4 3 5 main chain: pentane group: methyl (x1) 4 3 1 5 CH3 main chain: pentane group: methyl (x1) CH3 1 2 3 1 4 CH3 CH3 main chain: butane group: methyl (x2) 2 3 4 CH3 main chain: butane group: methyl (x2) 14 Naming more complex molecules Step 3: position of the group denoted by number of carbon of main chain that it is attached to. 4 2 1 3 5 2-methylpentane position of group name of group 2 1 3 main chain 5 4 2 3 1 4-methylpentane incorrect: start numbering from the end that gives groups the lowest number 4 5 3-methylpentane 15 Multiple groups 1 2 3 1 4 2,2-dimethylbutane 2 3 4 2,3-dimethylbutane there are 2 methyl groups group prefix di=2 tri=3 tetra=4 penta=5 hexa=6 16 Common Problems Be careful to choose the longest chain! 1 2 1 3 3 2 4 4 5 5 6 6 4-ethylheptane not 3-propylhexane 7 17 Numbering and priorities Always start numbering to give the lowest number for the first substituent: 2,3-dimethylpentane not 3,4-dimethylpentane 3,5,7-trimethyldecane not 3,6,8-trimethyldecane 18 5-ethyl-3-methyloctane not 4-ethyl-6-methyloctane not 3-methyl-5-ethyloctane 3/6 groups listed in alphabetical order 4-ethyl-2,8-dimethylnonane not 2,8-dimethyl-4-ethylnonane ignore “di-”, “tri-” etc. for alphabetical ordering 3-ethyl-6-methyloctane not 3-methyl-6-ethyloctane if same #s obtained in both directions, first group listed gets lower number 19 Groups within groups What happens when the alkyl group isn’t a straight chain? “isopropyl” (common name) “t-butyl” or “tert-butyl” (common name) “s-butyl” or “sec-butyl” (common name) 20 Treat branched side chains as groups with groups on them. Start numbering chain from point of attachment to main chain. 2 1-methylethyl group 1 4-(1-methylethyl)heptane 1 2 3 4 5 6 7 4-(1,1-dimethylethyl)heptane 5-(1-methylpropyl)nonane 21 Beyond alkanes Alkyl halides: compounds containing F, Cl, Br, I Br 1-bromobutane I I 1,1-diiodopropane Cl 2-chloropentane Fl 4-(1-fluoroethyl)heptane 22 Alcohols name of alkane--> replace “e” with “ol” OH OH ethanol OH 1-propanol or propan-1-ol 2-propanol or propan-2-ol OH HO 1,4-dihydoxybutane 23