Functional Groups Naming ALKANES There are some 15 important Functional Groups • (Hydrocarbons) = Alkanes, alkenes, alkynes, and aromatics. • (Single-bond Heteroatomic molecules) = Alkyl halides, ethers, amines, and sulfides. • (Simple carbonyls) = Ketone and Aldehyde • (Carboxylic derivatives) = Carboxylic acid, ester, amide, acid halide and nitriles. Identifying Functional Groups • When atoms are bonded together in specific arrangements, they undergo specific chemical reactions. • Such arrangements of atoms are called functional groups. 2-3 Summary of Important Families of Organic Compounds Ch. 2 - 4 Sulfides are missing – they are similar to alcohols since sulphur is in the same group as oxygen in the periodic table. sulfide/ thiol It’s important to identify functional groups. Firstly because the name is liked to the functional group, and secondly because the reactions and properties are typical of the functional group. Alkanes are the simplest organic functional group. They are also known as saturated hydrocarbons Saturated molecules only contain single bonds Hydrocarbons only contain H and C Nomenclature (IUPAC) The International Union of Pure and Applied Chemistry (IUPAC) is the international body responsible for setting up the system of “rules” for naming chemicals. Rule 1. Find the most important functional group to take the suffix (ending). In the IUPAC system the organic compound’s name is divided into a “prefix” a “parent” and a “suffix” 2 1 3 2-methylpropane PREFIX – tells you what substituents there are, how many and where they are situated in the molecule. PARENT – tells you how many carbons there are in the longest continuous carbon chain. SUFFIX – tells you what family (functional group) of organic compounds the compound belongs to. Most IMPORTANT functional group? IUPAC is a committee that decides regularly by consensus what functional groups are important. Mostly this is logical: More heteroatoms are usually more reactive and so are more multiple bonds. So Important confusing exception • Alkenes (double bond) are more important than alkynes (triple bond), but in naming compounds that have BOTH an alkENE and an alkYNE we use the term enyne. More about this later. Nomenclature of Alkanes 7 Rule 2. Use the longest continuous carbon chain as parent name, numbering the chain from one end to the other 6 5 4 3 CH3CH2CH2CH2CHCH3 2CH2 1 CH3 (3-Methylheptane) 6 5 4 3 2 1 CH3CH2CH2CH2CHCH3 NOT CH2 CH3 (2-Ethylhexane) Remember the IUPAC system is divided into a “prefix” a “parent” and a “suffix” 2 1 3 2-methylpropane The ending for all the names of alkanes is –ane The names of the longest chain stems from Greek and Latin usually one two three four five meth- eth- prop- but- pent- CH4 C 2H 6 C 3H 8 C4H10 C5H12 C6H14 methane ethane propane butane pentane hexane C7H16 C8H18 C9H20 heptane octane nonane C10H22 decane NOTE the – ane at the end of the name infers the family of the organic compound i.e. alkane “Straight-chain” (unbranched) alkanes Butane Pentane CH3CH2CH2CH3 CH3CH2CH2CH2CH3 These are the simplest structures that only have a SUFFIX and a PARENT, which is enough information to give EACH UNIQUE MOLECULE a UNIQUE NAME. The first 10 Unbranched or straight-chain alkanes. Name Structure Name Structure Methane CH4 Hexane CH3(CH2)4CH3 Ethane CH3CH3 Heptane CH3(CH2)5CH3 Propane CH3CH2CH3 Octane CH3(CH2)6CH3 Butane CH3CH2CH2CH3 Nonane CH3(CH2)7CH3 Pentane CH3(CH2)3CH3 Decane CH3(CH2)8CH3 These are sometimes also called “normal” alkanes (n-alkanes are a common name) If one hydrogen atom is removed from an alkane an alkyl group remains e.g. H H C H H methane H H C H methyl group Alkyl groups can be substituents in branched alkanes. A substituent is an atom or group of atoms that replace (substitute) a hydrogen atom in an organic molecule e.g. the methyl group and the OH group are BOTH substituents in the molecule 2- methylpropan-1-ol methyl group 2 1 OH alcohol functional group 2-methylpropan-1-ol Some common branched alkyl substituents CH3CH CH3 CH3CHCH2 CH3 Either 1-methylethylor isopropyl Either 2-methylpropylor isobutyl CH3CH2CH CH3 CH3 Either 1-methyl-1-propylor sec-butyl Either 1-methyl-2-propyl- CH3C or tert-butyl CH3 Nomenclature of Unbranched Alkyl substituents Alkyl group ● Removal of one hydrogen atom from an alkane Alkyl group (Cont’d) ● For an unbranched alkane, the hydrogen atom that is removed is a terminal hydrogen atom CH3 H CH3CH2 H CH3CH2CH2 H Methane Ethane Propane CH3 Methyl (Me) CH3CH2 Ethyl (Et) CH3CH2CH2 Propyl (Pr) Now we need more rules This is not a simple straight chain, n-alkane. Some parts of the molecule stick out from the chain and are substituents. The unsubstituted chain might look like this Can you spot the difference? If not, count the carbons. Rule 3. Number the chain from the side that gives the substituent the lowest number 4. Use the number obtained by Rule 3 to designate the location of the substituent along the chain. 7 6 5 4 3 CH3CH2CH2CH2CHCH3 2CH2 1 CH3 (3-Methylheptane) 1 2 3 4 5 CH3CH2CH2CH2CHCH3 NOT 6 CH2 7 CH3 (5-Methylheptane) Rule (Cont’d) 5. When two substituents are present on the same carbon, use that number twice 1 2 3 4 5 6 7 8 (4-Ethyl-4-methyloctane) Rule (Cont’d) 6. For two or more substituents, use the lowest possible individual numbers of the parent chain. (NOTE NOT THE TOTAL NUMBER) So 1,2,5-something is better than 2,6,7something. Similarly, 2,7,8-trimethyldecane not 3,4,9-trimethyl… (DON’T ADD 3+4+9=16 and say its better than 2+7+8=17) Rule (Cont’d) 6. Also, list all the substitutents alphabetically. In deciding alphabetical order, disregard multiplying prefix, such as “di”, “tri” etc. This sometimes gives a substituent with a higher number written before one with a lower number, but that’s OK. See the example on the next slide. Rule (Cont’d) 1 2 4 3 5 6 7 8 (6-Ethyl-2-methyloctane) NOT 8 7 6 5 4 NOT 3 2 1 1 2 3 4 5 6 7 8 (3-Ethyl-7-methyloctane) (2-Methyl-6-ethyloctane) Rule (Cont’d) 6. For identical substituents, use prefixes di-, tri-, tetra- and so on 6 5 4 3 2 1 (2,4-Dimethylhexane) NOT 1 7 6 5 4 3 2 1 (2,4,5-Trimethylheptane) NOT 2 3 4 5 6 (3,5-Dimethylhexane) 1 2 3 4 5 6 7 (3,4,6-Trimethylheptane) Rule (Cont’d) 7. When two chains of equal length compete for selection as parent chain, choose the chain with the greater number of substituents 7 6 5 4 3 2 1 4 NOT (2,3,5-Trimethyl4-propylheptane) 5 3 2 1 6 7 (only three substituents) Rule (Cont’d) 8. When branching first occurs at an equal distance from either end of the longest chain, choose the name that gives the lower number at the first point of difference 6 5 4 3 2 1 (2,3,5-Trimethylhexane) 1 NOT 2 3 4 5 6 (2,4,5-Trimethylhexane) Example 1 The most important functional group is alkane. Next find the longest chain as parent 4 5 3 6 2 7 1 4 or 3 5 2 6 1 7 Example 1 (Cont’d) ● Use the lowest numbering for substituents 4 3 ● 5 2 6 1 4 7 instead of 5 3 6 2 1 7 Substituents: two methyl groups dimethyl 4 3 5 2 6 1 7 Example 1 (Cont’d) ● Complete name 4 3 5 2 6 7 1 (3,4-Dimethylheptane) QUICK NOTE about dashes and commas. Use commas to separate numbers like 2,3,3 or 1,4,8 Use dashes to separate a number from a letter 1,2-dimethyl or 3-bromo-2,3diene Example 2 Example 2 (Cont’d) ● Find the longest chain as parent 6-carbon chain 8-carbon chain 8-carbon chain Example 2 (Cont’d) ● Find the longest chain as parent 9-carbon chain (correct!) ⇒ Nonane as parent Example 2 (Cont’d) ● Use the lowest numbering for substituents 7 8 3 9 5 2 1 3 6 4 (3,4,7) 2 1 5 instead of 8 9 7 4 6 (3,6,7) Example 2 (Cont’d) ● Substituents 3,7-dimethyl 4-ethyl 7 8 9 5 2 1 3 4 6 Example 2 (Cont’d) ● ● Substituents in alphabetical order Ethyl before dimethyl (recall Rule 5 – disregard “di”) Complete name 7 8 9 5 2 1 3 6 4 (4-Ethyl-3,7-dimethylnonane) Nomenclature of Branched Alkyl Substituents For most alkane substituents more than one alkyl group is possible For example in three-carbon groups (C3) Propyl Isopropyl (or 1-methylethyl) Four-carbon groups Butyl sec-butyl (1-methylpropyl) Isobutyl tert-butyl (or 1,1-dimethylethyl) Naming Practice Example 1 Clearly the ONLY Functional group is Alkane. Example 1 (Cont’d) ● Find the longest chain as parent (a) 6-carbon chain (b) 7-carbon chain (c) 8-carbon chain (d) 9-carbon chain Example 1 (Cont’d) ● Find the longest chain as parent (d) ⇒ Nonane as parent 1 2 3 4 5 6 7 8 9 or 9 8 7 6 5 4 3 2 1 Example 1 (Cont’d) ● 1 2 Use the lowest numbering for substituents 3 4 5 6 7 8 9 or 9 5,6 8 7 6 5 4 3 2 1 4,5 (lower numbering) ⇒ Use 4,5 Example 1 (Cont’d) ● Substituents Isopropyl (or 2-propyl) tert-butyl (or 2-methyl-2-propyl) 9 8 7 6 5 4 3 2 1 ⇒ 4-isopropyl and 5-tert-butyl Example 1 (Cont’d) ● Alphabetical order of substituents tert-butyl before isopropyl ● Complete name 9 8 7 6 5 4 3 2 1 5-tert-Butyl-4-isopropylnonane Example 2 Again the most important functional group is ALKANE, so ending is ……ANE Example 2 (Cont’d) ● Find the longest chain as parent (a) (b) 8-carbon chain (c) 9-carbon chain ⇒ Octane as parent 10-carbon chain 1 Example 2 (Cont’d) 2 3 4 5 6 7 8 9 10 or 10 9 8 7 6 5 4 3 2 1 Example 2 (Cont’d) ● Use the lowest numbering for substituents 5,6 1 2 3 4 5 6 7 8 9 10 or ⇒ Determined using the next Rules 10 9 5,6 8 7 6 5 4 3 2 1 Example 2 (Cont’d) ● Substituents sec-butyl Neopentyl But is it ● 5-sec-butyl and 6-neopentyl or ● 5-neopentyl and 6-sec-butyl ? Example 2 (Cont’d) ● Since sec-butyl takes precedence over neopentyl 5-sec-butyl and 6-neopentyl ● Complete name 10 9 8 7 6 5 4 3 2 1 5-sec-Butyl-6-neopentyldecane The sec- and tert- are abbreviations of the secondary and tertiary classification of carbon atoms. Primary C is bonded to ONE other C Secondary C is bonded to TWO other C Tertiary C is bonded to THREE other C Quaternary C is bonded to FOUR other C Naming compounds with other functional groups is not much different…. Alcohols (R-OH) use the prefix “hydroxy” OR the suffix “ol” OH 4 1 2 3 2-hydroxy-3-methylbutane OR 3-methylbutan-2-ol Amines (R-NH2) use the prefix “amino” OR the suffix “amine” NH2 4 1 2 3 2-amino-3-methylbutane OR 3-methylbutan-2-amine Alkyl halides (R-X e.g. where X = chlorine) use the prefix “chloro” OR the suffix “-yl chloride” Cl 4 1 2 3 2-chloro-3-methylbutane OR 3-methyl-2-butyl chloride A few more examples – do you agree with the numbers? 1 2 3 4 3 2 CH3 1 5 4 3 2 1 HOCH2CH2CH2Br ClCH2CH2CHCH3 CH3CCH2CHCH3 3-bromo-1-propanol OH 4-chloro-2-butanol CH3 OH 4,4-dimethyl-2-pentanol What about these examples? CH3 CH3CHCHCH2CH3 Cl OH 2-chloro-3-pentanol not 4-chloro-3-pentanol CH3CH2CH2CHCH2CHCH3 OH CH3 2-methyl-4-heptanol not 6-methyl-4-heptanol OH 3-methylcyclohexanol not 5-methylcyclohexanol A few more complex ones to show that the substituents are listed in alphabetical order CH2CH3 CH2CH3 CH3CHCH2CHCH2CHCH3 Br H 3C OH 6-bromo-4-ethyl-2-heptanol OH 2-ethyl-5-methylcyclohexanol HO CH3 CH3 3,4-dimethylcyclopentanol Nomenclature of Amines 1 4 3 2 1 2 3 4 5 3 6 CH3CH2CHCHCH2CH3 CH3CH2CH2CH2NH2 NHCH2CH3 1-butanamine or butan-1-amine N-ethyl-3-hexamine or N-ethylhexan-3-amine 2 1 CH3CH2CH2NCH2CH3 CH3 N-ethyl-N-methyl-1-propanamine or N-ethyl-N-methylpropan-1-amine • The substituents are listed in alphabetical order and a number or an “N” is assigned to each one 4 3 2 1 1 2 3 CH3 4 5 Br 6 CH3CH2CHCHCHCH3 CH3CHCH2CH2NCH3 NHCH2CH3 Cl 3-chloro-N-methyl-1-butanamine N-ethyl-5-methyl-3-hexanamine CH2CH3 NHCH2CH2CH3 2-ethyl-N-propylcyclohexanamine 5 4 3 2 1 CH3CHCHCHCH3 N H3C CH3 4-bromo-N,N-dimethyl-2-pentanamine