Branched-Chain Alkanes

1. Branched-Chain Alkanes • Branched-chain means that other elements besides hydrogen may be attached to the carbon • hydrocarbon, halogens, oxygen, nitrogen, sulfur, etc. • any atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branchedpart

2. Branched-Chain Alkanes • A hydrocarbon substituent is called an alkyl group • use the same prefixes to indicate the number of carbons, but the -ane ending is now -yl • methyl, ethyl, propyl, etc.

3. Alkyl Groups Branches on carbon chains H H C CH3 methyl H H H H C C CH3CH2 ethyl H H

4. Branched Alkanes CH3 CH3CHCH3 methyl groups CH3 CH3 CH3CHCH2CHCH3

5. Steps for naming Branched-Chain Alkanes p.247-248 1. Count the C’s in the longest chain (parent chain) 2. Number parent chain so branches have lowest possible number 3. Name each branch 4. Use prefix for more than one branch on the same carbon 5. Alphabetize branches 6. Use proper punctuation ( - , )

6. Naming Branched Alkanes CH3 methyl branch CH3CH2CH2CHCH2CH3 6 5 4 3 2 1 Count

7. Naming Branched Alkanes CH3 methyl branch CH3CH2CH2CHCH2CH3 6 5 4 3 2 1 Count 3-Methylhexane on third C CH3 six carbon chain group

8. Learning Check A. CH3CH3 CH3CHCH2CHCH3 B. CH3 CH3 CH3CH2CHCH2CCH2CH3 CH3

9. Solution A. CH3CH3 CH3CHCH2CHCH3 2,4-dimethylpentane B. CH3 CH3 CH3CH2CHCH2CCH2CH3 CH3 3,3,5-trimethylheptane

10. Branched-Chain Alkanes • From the name, draw the structure: 1. Find the parent, with the -ane 2. Number carbons on parent 3. Identify substituent groups; attach 4. Add remaining hydrogens

11. Learning Check Write a condensed structure for A. 3,4-dimethylheptane B. 2,2-dimethyloctane

12. Solution • 3,4-dimethylheptane CH3 CH3CH2CHCHCH2CH2CH3 CH3

13. Solution • 2,2-dimethyloctane CH3 CH3CCH2CH2CH2CH2CH2CH3 CH3

14. Learning Check Write a condensed structure for A. 3-ethylpentane B. 2,3,4-trimethylhexane