OCHEM Exam 2 Study Guide ST - CHAPTER 4 4.2 Nomenclature of...

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CHAPTER 4 4.2 Nomenclature of Alkanes Systemic names Names produced by IUPAC rules Substituents Groups connected to the parent chain If there is a competition between two chains of equal length -- chose the chain with the greater number of substituents Cycloalkanes “Cyclo-” indicates the presence of a ring Naming Substituents Named with the same terminology as naming parents but add “-yl” Alkyl Groups Substituent with two carbon atoms (ethyl) Naming Complex Substituents Place numbers going away from the parent chain Treat complex substituents as if it has a miniparent with it’s own substituents Assembling the Systematic Name of an Alkane Locant Location of the methyl group clearly identified with a number Naming Alkanes 1. Identify the parent chain 2. Identify and name the substituents 3. Number the parent chain and assign a locant to each substituent 4. Arrange the substituents alphabetically
Naming Bicyclic Compounds Bridgeheads: two carbon atoms where the rings are fused together For each path, count the # of carbons (excluding bridgeheads) To number the parent - start at one of the bridgeheads and begin numbering along the longest path, then go to the 2nd longest path, finally go along the shortest path Strategy For Naming Complex Compounds 1. Identify the parent 2. Identify and name substituents 3. Assign locants
4. Arrange substituents alphabetically Constitutional Isomers Number of possible constitutional isomers increase with increasing molecular size Tip for not drawing same molecule - compare names Relative Stability (Heat of Combustion) Change in enthalpy: heat given off during the reaction ( H°) For a combustion process - H° is called the heat of combustion Increases with each CH 2 group Compare rings of different sizes by dividing the HOC by # of CH 2 groups in the compound Gives HOC per CH 2 group Differences in H° can be found by comparing stability of alkanes Compare amount of heat given off by each combustion process Compare potential energy that each isomer had before combustion Branched alkanes are LOWER in energy (MORE STABLE) than straight-chain alkanes Branched = more stable = lower energy Newman Projections Conformations: 3D shapes Steps to drawing

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