Ch.3 Organic Compounds: Alkanes and Cycloalkanes 3.1 Functional Groups • more than 19 million known organic compounds according to Chemical Abstracts • classify into families with similar chemical behavior functional groups: a group of atoms within a molecule that has a characteristic chemical behavior ; a given functional group, regardless of size and complexity, behaves in nearly the same way Ch.3 Organic Compounds: Alkanes and Cycloalkanes Br H H Br2 H H H H H BrH Ethylene Br2 HO HO Br Cholesterol Br Ch.3 Organic Compounds: Alkanes and Cycloalkanes Functional Groups C/C Multiple Bonds C-Y (Y= electronegative atom: O, N, Cl, S...) C=O, C=N, C≡N Functional Groups with C/C Multiple Bonds CC CC CC Alkane Alkene Alkyne Arene (aromatic ring) Ch.3 Organic Compounds: Alkanes and Cycloalkanes Functional Groups with C-Y (Y= electronegative atom) C X C OH CCO (X= F, Cl, Br, I) Halide Alcohol Ether C NH2 CSSH CC Amine Thiol Sulfide Ch.3 Organic Compounds: Alkanes and Cycloalkanes Functional Groups with C=O O O O CHC CCC COHC Aldehyde Ketone Carboxylic acid O O O COC C CNC CClC Ester Amide Carboxylic acid chloride Ch.3 Organic Compounds: Alkanes and Cycloalkanes Table 3.1 Structures of Common Functional Groups Family Functional group Simple example Name ending name structure contains only C-H and -ane Alkane CH CH C-C single bonds 3 3 Ethane -ene Alkene CC CH2=CH2 Ethene (Ethylene) -yne Alkyne CC HHCC Ethyne (Acetylene) None Arene Benzene Ch.3 Organic Compounds: Alkanes and Cycloalkanes Table 3.1 Structures of Common Functional Groups Family Functional group Simple example Name ending name structure None Halide C X (X= F, Cl, Br, I) H C Cl 3 Chloromethane -ol Alcohol C OH H C OH 3 Methanol -ether Ether C O C H C O CH 3 3 Dimethyl ether Ch.3 Organic Compounds: Alkanes and Cycloalkanes Table 3.1 Structures of Common Functional Groups Family Functional group Simple example Name ending name structure -amine Amine C NH C NH C N H3C NH2 2 Methylamine -nitrile Nitrile C C N H3C C N Ethanenitrile (Acetonitrile) None Nitro C NO H C NO 2 3 2 Nitromethane Ch.3 Organic Compounds: Alkanes and Cycloalkanes Table 3.1 Structures of Common Functional Groups Family Functional group Simple example Name ending name structure -thiol Thiol C SH H C SH 3 Methanethiol -sulfide H CCHS Sulfide CCS 3 3 Dimethyl sulfide O O -sulfoxide H CCHS Sulfoxide CCS 3 3 Dimethyl sulfoxide O O -sulfone H CCHS Sulfone CCS 3 3 Dimethyl sulfone O O Ch.3 Organic Compounds: Alkanes and Cycloalkanes Table 3.1 Structures of Common Functional Groups Family Functional group Simple example Name ending name structure O O -al Aldehyde CHC Ethanal H3CHC (Acetaldehyde) O O -one Ketone CCC Propanone H3CCHC 3 (Acetone) O O -oic acid Carboxylic COHC Ethanoic acid acid H3COHC (Acetic acid) O O -oate Ester COC C Methyl ethanoate H3COC CH3 (Methyl acetate) Ch.3 Organic Compounds: Alkanes and Cycloalkanes Table 3.1 Structures of Common Functional Groups Family Functional group Simple example Name ending name structure O O O O -amide Amide CNHC 2 CNHC CNC Ethanamide H3CNHC 2 (Acetamide) O O -oyl chloride Carboxylic CClC Ethanoyl chloride acid chloride H3CClC (Acetyl chloride) O O O O -oic anhydride Carboxylic COC C C Ethanoic anhydride acid anhydride H3COC CCH3 (Acetic anhydride) Ch.3 Organic Compounds: Alkanes and Cycloalkanes Practice functional Groups O O O HO O Coleophomone A Ch.3 Organic Compounds: Alkanes and Cycloalkanes 3.2 Alkanes and Alkane Isomers alkanes: saturated hydrocarbon, : aliphatic compound (meaning "fat") general formula: CnH2n+2 H CCH CH CH CH CH4 3 3 3 2 3 Methane Ethane, C2H6 Propane, C3H8 C4H10 Butane Isobutane (2-Methylpropane) Ch.3 Organic Compounds: Alkanes and Cycloalkanes C5H12 Pentane 2-Methylbutane 2,3-Dimethylpropane Ch.3 Organic Compounds: Alkanes and Cycloalkanes - straight chain alkanes (normal alkane) - branched chain alkane Pentane 2-Methylbutane 2,3-Dimethylpropane C5H12 isomer: same formula but different structure constitutional isomer: connected differently Ch.3 Organic Compounds: Alkanes and Cycloalkanes Practice How many isomers ? C6H14 5 Ch.3 Organic Compounds: Alkanes and Cycloalkanes - constitutional isomerism is not limited to alkanes Different carbon skeleton Butane Isobutane C4H10 (2-Methylpropane) Different functional CH3CH2OH CH3OCH3 group Ethyl alcohol Diethyl ether C2H6O NH2 CH CH CH NH Different position of CH3CHCH3 3 2 2 2 functional group Ethyl alcohol Propylamine C3H9N Ch.3 Organic Compounds: Alkanes and Cycloalkanes - different ways to represent n-butane (n= normal); n-C4H10 H H H H HCC C C H H3CCH2 CH2 CH3 CH3CH2CH2CH3 H H H H HHHH H C C CH3(CH2)2CH3 C C H HHH H these structures do not imply any specific geometry Ch.3 Organic Compounds: Alkanes and Cycloalkanes Names of straight chain alkanes: ending -ane 1 Methane 9 Nonane 2 Ethane 10 Decane 3 Propane 11 Undecane 4 Butane 12 Dodecane 5 Pentane 13 Tridecane 6 Hexane 20 Icosane 7 Heptane 21 Henicosane 8 Octane 30 Triacotane Ch.3 Organic Compounds: Alkanes and Cycloalkanes 3.3 Alkyl Groups alkyl group: partial structure of alkane (-H); used for naming purpose H C NH CH4 H3C H3C OH 3 2 Methane A methyl group Methyl alcohol Methyl amine -CH CH CH CH -CH3 -CH2CH3 -CH2CH2CH3 2 2 2 3 Methyl (Me) Ethyl (Et) Propyl (Pr) Butyl (Bu) -CH2CH2CH2CH2CH3 Pentyl, or Amyl Ch.3 Organic Compounds: Alkanes and Cycloalkanes Propyl (n-Pr) Isopropyl (i-Pr) n-Butyl (n-Bu) sec-Butyl (s-Bu) Isobutyl (i-Bu) tert-Butyl (t-Bu) Ch.3 Organic Compounds: Alkanes and Cycloalkanes four possible degrees of alkyl substitution for carbon H H R C H R C H H R primary carbon (1o) secondary carbon (2o) R R R C H RRC R R tertiary carbon (3o) quartenary carbon (4o) R = a generalized alkyl group Ar = a generalized aryl group Ch.3 Organic Compounds: Alkanes and Cycloalkanes H H R R C OH R C OH R C OH H R R o primary alcohol (1o) secondary alcohol (2o) tertiary alcohol (3 ) CH 3 primary hydrogens CH3CH2CHCH3 a tertiary hydrogen secondary hydrogens Ch.3 Organic Compounds: Alkanes and Cycloalkanes 3.4 Naming Alkanes IUPAC: International Union of Pure and Applied Chemistry Prefix Parent Suffix Where are the substituents? How many carbons? What family? Ch.3 Organic Compounds: Alkanes and Cycloalkanes Step 1. Find the parent hydrocarbon. a) the longest continuous chain of carbon atoms hexane heptane Ch.3 Organic Compounds: Alkanes and Cycloalkanes b) if two different chains of equal length are present ; choose the one with the larger number of branch points two substituents one substituents Ch.3 Organic Compounds: Alkanes and Cycloalkanes Step 2. Number the atoms in the main chain. a) beginning at the end nearer the first branch point 1 6 3 2 4 5 7 heptane 7 2 4 NOT 6 4 3 1 Ch.3 Organic Compounds: Alkanes and Cycloalkanes b) if there is branching an equal distance away from both ends; begin the end nearer the second branch point 8 6 2 2 4 8 7 3 1 3 7 9 9 4 1 6 5 5 3,4,7 3,6,7 NOT Ch.3 Organic Compounds: Alkanes and Cycloalkanes Step 3. Identify and number the substituents. a) assign a number to each substituent according to its point of attachment to the main chain 8 6 2 7 3 1 3-ethyl 9 4 5 4-methyl 7-methyl a nonane Ch.3 Organic Compounds: Alkanes and Cycloalkanes b) If there are two substituents on the same carbon, give them both the same number. 6 3 1 2-methyl 4 2 5 4-methyl 4-ethyl a hexane Ch.3 Organic Compounds: Alkanes and Cycloalkanes Step 4. Write the name as a single word. -use hyphens to seperate the different prefixes -use comma to seperate numbers -cite in alphabetical order - more than one identical substituents; di-, tri-, tetra-... (Don't use these prefixes for alphabetizing purposes) 3 3- Methylhexane 8 6 2 7 3 1 9 4 3-Ethyl-4,7-dimethylnonane 5 Ch.3 Organic Compounds: Alkanes and Cycloalkanes Me 3 2 3-Ethyl-2-methylheptane Et 4-Ethyl-3-methyloctane 4-Ethyl-2,4-dimethylheptane Ch.3 Organic Compounds: Alkanes and Cycloalkanes Step 5. Name a complex substituent just as though it were itself a compound. 8 1 3 7 10 2 4 6 5 9 2,3,6-trisubstituted decane Ch.3 Organic Compounds: Alkanes and Cycloalkanes - begin numbering at the point of attachment Molecule 2 3 1 2-methylpropyl group Ch.3 Organic Compounds: Alkanes and Cycloalkanes The substituent is alphabetized according to the first letter of its complete name (including any numerical prefix) and is set off in parentheses. 8 1 3 7 10 2 4 6 5 9 2,3-Dimethyl-6-(2-methylpropyl)decane 6-Isobutyl-2,3-dimethyldecane Ch.3 Organic Compounds: Alkanes and Cycloalkanes - alphabetizing the substituent: the first letter of the complete name (including any numerical prefix of the complex substituent) 8 1 3 5 7 2 4 6 9 1 5-(1,2-dimethylpropyl) 3 2 2-methyl 5-(1,2-Dimethylpropyl)-2-methylnonane Ch.3 Organic Compounds: Alkanes and Cycloalkanes Practice IUPAC Name 6-(1-ethylbutyl) 6 6-(1-Ethylbutyl)-3,5-dimethylundecane Ch.3 Organic Compounds: Alkanes and Cycloalkanes common names: historical reason three-carbon alkyl group Isopropyl (i-Pr) four-carbon alkyl group sec-Butyl (s-Bu) Isobutyl (i-Bu) tert-Butyl (t-Bu) Ch.3 Organic Compounds: Alkanes and Cycloalkanes five-carbon alkyl group Isopentyl or Neopentyl tert-Pentyl or isoamyl (i-amyl) tert-amyl (t-amyl) Ch.3 Organic Compounds: Alkanes and Cycloalkanes common name and IUPAC name, both are used 4-(1-Methylethyl)octane or 4-Isopropyloctane Caution iso, neo, cyclo are considered part of the alkyl-group for alphabetizing purposes but sec-, tert- are not.