Isomers

C11-5-14 NAMING AND DRAWING Vocabulary & Concepts Structural isomers OUTCOME QUESTION(S): C11-5-14 NAMING AND DRAWING Name and draw structural models of simple and branched alkanes. Include: complete structural formula, molecular formula, general formula, isomers Name and draw structural models of simple and branched alkenes and alkynes. Compare and contrast the structure and uses of aromatic and aliphatic hydrocarbons. Vocabulary & Concepts Structural isomers

Isomer: Compounds with the same molecular formula but different arrangement of bonded atoms. Like all concepts this course – we are just scratching the surface – the same with isomers…we will focus on structural isomers only (C3H7F) (C3H7F)

Carbon atoms in alkanes can rotate (twist) freely around in the single bonds. Don’t believe it? Follow the rules and name them both… C - C C C - C - C - C C C - C - Which means these two compounds are really the exact same. Structural isomer: a constitutional isomer in which molecules have the same molecular formula but a different organization of atoms.

C4H10 Draw butane and 2-methylpropane. C H3 C – C – C – C H3 H2 H2 H3 structural isomers

They all look different…name them to be sure Draw and name 2 different structural isomers for a pentane. C - C C C - C - C C C - C - They all look different…name them to be sure 2-methylbutane 2,2-dimethylpropane C - C C C - C - C - C C C - C - 2-methylbutane pentane Common mistakes Counting from the wrong end Bent parent chains Wrong parent chain Branching off the end carbon

Obviously, the more carbon atoms – the more structural isomers* Octane (C8H18) - 18 structural isomers Decane (C10H22) - 75 structural isomers Eicosane (C20H42) - 366 319 structural isomers! *Cycloalkanes are not considered isomers: 4 1 C – C – C – C H3 H2 H2 H3 H2 C H2 1 2 3 4 3 butane H2 H2 C4H10 2 cyclobutane With the connecting end carbons - cycloalkanes have too few hydrogen C4H8

C9H20 3-ethyl-2-methylhexane C H3 The alkane with 9 carbons is nonane. 3-ethyl-2-methylhexane is a structural isomer of which straight chained alkane? Remember: isomers have the same number of carbons – so just use that… 3-ethyl-2-methylhexane 2 carbon 1 carbon 6 carbon 2 carbons + 1 carbons + 6 carbon = 9 carbons C H3 The alkane with 9 carbons is nonane. C H3 H2 C9H20 C – C – C – C – C – C H3 H H H H2 H3 1 2 3 4 5 6

Present in unhealthy “trans fats” Stereoisomer: a specific type of isomer with a different spatial arrangement around the double bond. (Carbons can’t rotate around in double bonds) Commonly called Cis/Trans isomers (C4H8) (C4H8) cis form trans form Present in unhealthy “trans fats”

Make a prediction of how branching may affect this property Melting/Boiling Points Isomers show a decrease in melting/boiling point with increased branching. Branching creates space  weakens IMF  lowers energy needs Make a prediction of how branching may affect this property C6H14 Name Boiling Point Linear Hexane 69oC 1 branch 2-methylpentane 60oC 2 branches 2,2-dimethylbutane 50oC linear alkane branched alkane

C11-5-14 NAMING AND DRAWING Vocabulary & Concepts Structural isomers CAN YOU / HAVE YOU? C11-5-14 NAMING AND DRAWING Name and draw structural models of simple and branched alkanes. Include: complete structural formula, molecular formula, general formula, isomers Name and draw structural models of simple and branched alkenes and alkynes. Compare and contrast the structure and uses of aromatic and aliphatic hydrocarbons. Vocabulary & Concepts Structural isomers