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Chapter 3 Organic Compounds: Alkanes and their Stereochemistry

Chapter 3 Organic Compounds: Alkanes and their Stereochemistry. Functional Groups – See Table 3.1 in McMurry Be able to recognize: alkene, alkyne, aromatic (arene), halide, alcohol, ether, amine, aldehyde, ketone, carboxylic acid, ester, amide, acid chloride, acid anhydride, others.

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Chapter 3 Organic Compounds: Alkanes and their Stereochemistry

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  1. Chapter 3 Organic Compounds: Alkanes and their Stereochemistry Functional Groups – See Table 3.1 in McMurry Be able to recognize: alkene, alkyne, aromatic (arene), halide, alcohol, ether, amine, aldehyde, ketone, carboxylic acid, ester, amide, acid chloride, acid anhydride, others

  2. Hydrocarbons Contain Only Carbon and Hydrogen Alkanes Single carbon-carbon bonds Saturated Alkenes Double carbon-carbon bonds Unsaturated Alkynes Triple carbon-carbon bonds Unsaturated Aromatics Ring of alternating single and Unsaturated double bonds

  3. Saturated versus Unsaturated Hydrocarbons Saturated Maximum possible number of hydrogens per carbon atom Only C-C and C-H single bonds Formula CnH2n+2 Example: CH3CH3 (ethane) Unsaturated Contain fewer hydrogen atoms than corresponding saturated compound May have double or triple bond(s) or ring(s) Example: CH2CH2 (ethene)

  4. Alkanes Only C-H and C-C single bonds General formula: CnH2n+2 Generally unreactive; can undergo combustion or radical halogenation Useful as fuels Hydrophobic (lipophilic) since C-H and C-C bonds are nonpolar Propane CH3CH2CH3

  5. Nomenclature: Parent Indicates Number of Carbons Number of C atomsParent 1 meth 2 eth 3 prop 4 but 5 pent 6 hex 7 hept 8 oct 9 non 10 dec

  6. Nomenclature of Linear Alkanes Suffix “ane” indicates alkane. Molecular FormulaAlkane CH4 methane CH3CH3 ethane CH3CH2CH3 propane CH3CH2CH2CH3 butane CH3CH2CH2CH2CH3 pentane CH3CH2CH2CH2CH2CH3 hexane CH3CH2CH2CH2CH2CH2CH3 heptane CH3CH2CH2CH2CH2CH2CH2CH3 octane CH3CH2CH2CH2CH2CH2CH2CH2CH3 nonane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 decane Linear (“normal” alkanes depicted above – isomers exist for alkanes with 4 or more C atoms.

  7. Constitutional Isomers: Same Molecular Formula, Different Connectivity There is more than one structure for C5H12. n-pentane (“normal” pentane) is linear: CH3CH2CH2CH2CH3 Can also draw branched structures for C5H12. Draw other structures for C5H12

  8. Constitutional Isomers of C5H12 n-pentane (C5H12) iso-pentane (C5H12) neo-pentane (C5H12) Isomers are different compounds that have the same molecular formula. Constitutional isomers: Same molecular formula, different bond connectivity.

  9. Constitutional Isomers are Different Compounds with Different Properties Constitutional isomers may have different functional groups (e.g. ether and alcohol).

  10. Alkyl Groups Alkyl groups are partial structures, where the hyphen indicates its connection point to the remainder of the molecule. Alkyl groupNameAbbreviation -CH3 methyl Me -CH2CH3 ethyl Et -CH2CH2CH3 propyl Pr -CH2CH2CH2CH3 butyl Bu -CH2CH2CH2CH2CH3 pentyl (amyl)

  11. Alkyl Groups, continued The “squiggly” line indicates the connection point to the rest of the molecule.

  12. Primary, Secondary, Tertiary and Quaternary Carbons Primary (1°) carbon is bonded to one other carbon. Secondary (2°) carbon is bonded to two other carbons. Tertiary (3°) carbon is bonded to three other carbons. Quaternary (4°) carbon is bonded to four other carbons. 2° C 4° C 1° C

  13. Generalized Organic Groups (Generics) R General organic group, connecting via a carbon atom Example: methyl (Me), ethyl (Et), tert-butyl (tBu) Ar General aromatic group Example: phenyl (Ph) X Halogen – F, Cl, Br or I

  14. IUPAC Nomenclature – General Guidelines for Alkanes IUPAC = International Union of Pure and Applied Chemistry • Locant-prefix-parent-suffix • Assign the longest chain of carbon atoms (parent) with suffix “ane” (suffix) for alkanes. If more than one possible chain, chose chain with more branching. • 2. Number atoms in the longest chain so substituents have the lowest values. • Name the substituents (prefix) and number their positions in chain (locant). • Write the name as a single word locant - position of substituents prefix - substituents parent - longest carbon chain suffix - primary functional group

  15. IUPAC Nomenclature – Additional Guidelines • Substituents are listed in alphabetical order. Di, tri, and tetra are not counted, though iso, sec and tert are. • 4-chloro-2-methylhexane • 4-isopropyl-3,3-dimethyloctane • Parentheses are used for complex substituents • chloromethylbenzene (can be ortho-, meta- or para- substituted) • (chloromethyl)benzene (also referred to as benzyl chloride)

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