Organic Nomenclature: Naming Organic Molecules Mild Vegetable Alkali Aerated Alkali What’s in a name? Tartarin Glauber's Alkahest Alkahest of Van Helmot Fixed Vegetable Alkali Russian Pot Ash Cendres Gravellees Alkali Mild Vegetable Oil of Tartar Pearl Ash Tartar Alkahest of Reapour K2CO3 Alkali of Reguline Caustic Sal Juniperi Potassium Carbonate Ash ood Alkali of Wine Lees Salt of Tachenius W Fixed Sal Tartari Sal Gentianae Alkali Salt German Ash Salt of Wormwood Cineres Clavellati Sal Guaiaci exSal Ligno Alkanus Vegetablis IUPAC Rules for naming organic molecules International Union of Pure and Applied Chemists 3 Name Molecular Prefix Formula Methane CH4 Meth Ethane C2H6 Eth Alkanes Propane C3H8 Prop Butane C4H10 But CnH2n+2 Pentane C5H12 Pent Hexane C6H14 Hex Heptane C7H16 Hept Octane C8H18 Oct Nonane C9H20 Non Decane C10H22 Dec 4 Structure of linear alkanes propane butane pentane hexane heptane octane nonane 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 n # of isomers 1 1 2 1 The more carbons in a 3 1 molecule, the more 4 2 possible ways to put 5 3 them together. 6 5 7 9 8 18 9 35 10 75 15 4,347 25 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 4 6 longest chain = 6 (hexane) 1 3 5 2 4 3 4 3 2 2 1 5 4 1 3 5 correct 1 incorrect longest chain = 5 (pentane) longest chain = 5 (pentane) 1 3 1 2 2 3 4 4 longest chain = 4 (butane) 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 4 4 3 2 1 5 1 3 5 CH3 main chain: pentane main chain: pentane CH3 1 3 1 2 2 3 4 4 CH3 CH3 CH3 main chain: butane main chain: butane 11 Alkyl groups: fragments of alkanes H H empty space (point where it H C H H C attaches to something else) H H methane methyl CH4 CH3 12 More generally... H H H H H H H H H H C C H C C C H C C C C H H H H H H H H H ethyl propyl butyl C2H5 C3H7 C4H9 CnH2n+1 13 Naming more complex molecules CH3 2 4 4 3 2 1 5 1 3 5 CH3 main chain: pentane main chain: pentane group: methyl (x1) group: methyl (x1) CH3 1 3 1 2 2 3 4 4 CH3 CH3 CH3 main chain: butane main chain: butane group: methyl (x2) 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 2 4 1 3 5 5 3 1 2-methylpentane 4-methylpentane incorrect: start numbering from position name of main the end that gives groups the of group group chain lowest number 2 4 3 1 5 3-methylpentane 15 Multiple groups 1 3 1 2 2 3 4 4 2,2-dimethylbutane 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 4-ethylheptane 2 3 not 3 5 1 2 4 6 3-propylhexane 4 6 5 7 17 Numbering and priorities Always start numbering to give the lowest number for the first substituent: 2,3-dimethylpentane 3,5,7-trimethyldecane not 3,4-dimethylpentane not 3,6,8-trimethyldecane 18 5-ethyl-3-methyloctane groups listed in not 4-ethyl-6-methyloctane alphabetical not 3-methyl-5-ethyloctane order ignore “di-”, “tri-” 4-ethyl-2,8-dimethylnonane etc. for not 2,8-dimethyl-4-ethylnonane alphabetical ordering if same #s obtained in both 3-ethyl-6-methyloctane directions, first not 3-methyl-6-ethyloctane group listed gets 3/6 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 2 4 6 1 3 5 7 4-(1,1-dimethylethyl)heptane 5-(1-methylpropyl)nonane 21 Beyond alkanes Alkyl halides: compounds containing F, Cl, Br, I Br Cl 1-bromobutane 2-chloropentane Fl I I 4-(1-fluoroethyl)heptane 1,1-diiodopropane 22 Alcohols name of alkane--> replace “e” with “ol” OH OH OH ethanol 1-propanol 2-propanol or or propan-1-ol propan-2-ol OH HO 1,4-dihydoxybutane 23.