principles and modern applications Chemistry 140 Fall 2002 ELEVENTH EDITION GENERAL CHEMISTRY principles and modern applications PETRUCCI HERRING MADURA BISSONNETTE 26 Structures of Organic Compounds PHILIP DUTTON UNIVERSITY OF WINDSOR DEPARTMENT OF CHEMISTRY AND BIOCHEMISTRY

Structures of Organic Compounds Chemistry 140 Fall 2002 Structures of Organic Compounds CONTENTS 26-1 Organic Compounds and Structures: An Overview 26-2 Alkanes 26-3 Cycloalkanes 26-4 Stereoisomerism in Organic Compounds 26-5 Alkenes and Alkynes 26-6 Aromatic Hydrocarbons 26-7 Organic Compounds Containing Functional Groups 26-8 From Molecular Formula to Molecular Structure

Representations of the methane molecule Chemistry 140 Fall 2002 26-1 Organic Compounds and Structures: An Overview FIGURE 26-1 Representations of the methane molecule

Chemistry 140 Fall 2002 FIGURE 26-2 The ethane molecule C2H6

The propane molecule, C3H8 Chemistry 140 Fall 2002 FIGURE 26-3 The propane molecule, C3H8

Constitutional Isomers in Organic Compounds Chemistry 140 Fall 2002 Constitutional Isomers in Organic Compounds

Line-angle formulas or line structures

Nomenclature Select the longest continuous carbon chain. Every branch is considered an alkyl group. Number the base chain so substituents appear at the lowest numbers possible . Name each substituent according to its identity, use di, tri, tetra, and so on. Separate numbers with commas but no spaces and numbers from letters with hyphens. List substituents alphabetically, prefixes are ignored.

Functional groups

26-2 Alkanes Saturated hydrocarbons: Only single bonds. Normal formula is CnH2n+2 Branching of chains affects properties.

Staggered conformation of ethane Chemistry 140 Fall 2002 Conformations FIGURE 26-5 Staggered conformation of ethane

Staggered and eclipsed conformations of ethane Chemistry 140 Fall 2002 FIGURE 26-6 Staggered and eclipsed conformations of ethane

The dihedral angle, θ, refers to the angle of rotation about a carbon-carbon bond.

Chemistry 140 Fall 2002 The barrier to rotation is small enough a room FIGURE 26-7 Potential energy diagram for the internal rotation of the methyl groups in ethane

Steric hinderance in a totally eclipsed conformation of butane FIGURE 26-9 Steric hinderance in a totally eclipsed conformation of butane

FIGURE 26-8 Conformations and their potential energies of butane for rotation about the C2-C3 bond

Preparation of Alkanes (26.1) (26.2) (26.3)

Alkanes from petroleum

2,2,4-Trimethylpentane Octane rating: 100 n-Heptane Octane rating: 0 A catalytic cracking unit (cat cracker) at a petroleum refinery

26-3 Cycloalkanes CnH2n

Ring strain in cyclopropane Chemistry 140 Fall 2002 Ring Strain in Cycloalkanes FIGURE 26-10 Ring strain in cyclopropane

Newman projection for cyclopropane FIGURE 26-11 Newman projection for cyclopropane

Two important conformations of cyclohexane Chemistry 140 Fall 2002 Cis-Trans Isomerism in Distributed Cycloalkanes FIGURE 26-12 Two important conformations of cyclohexane

Chemistry 140 Fall 2002

A Closer Look at Cyclohexane 1. 4. Points upward 2. Points downward Imaginary line through the center of the ring 3. 5.

The interconversion of two chair conformations in cyclohexane Chemistry 140 Fall 2002 In the figure, two of the H atoms are shown in red to emphasize that when the cyclohexane ring converts from one chair conformation to another, the equatorial hydrogen atoms are converted into axial hydrogen atoms and vice versa. The interconversion of the two chair forms proceeds through other conformations, including the boat form. FIGURE 26-13 The interconversion of two chair conformations in cyclohexane

26-4 Stereoisomerism in Organic Compounds FIGURE 26-14 Isomerism summarized

Chirality

Nonsuperimposable mirror images of 3-methylhexane Chemistry 140 Fall 2002 FIGURE 26-15 Nonsuperimposable mirror images of 3-methylhexane

Assignment of R and S configuration at a tetrahedral stereocenter Chemistry 140 Fall 2002 Naming Enantiomers: The R, S System of Nomenclature FIGURE 26-16 Assignment of R and S configuration at a tetrahedral stereocenter

Rules for Assigning Priorities to Substituents Rule 1: Substituent of higher atomic number takes precedence over one of lower atomic number:

Rule 2: If two substituents attached to the stereocenter have the same priority, proceed along the chains to the first point of difference:

Rule 3: Double and triple bonds count as if they were single and the atoms are duplicated or triplicated at the other end of the double or triple bond:

26-5 Alkenes and Alkynes

Stereoisomerism in Alkenes

Preparation and Uses of Alkenes and Alkynes Elimination reaction

Simple qualitative test for an alkene (26.8) The test tube on the left contains cyclohexene and the one on the right contains cyclohexane. When bromine, Br2, is added to the tube containing cyclohexene, the red-brown color disappears because Br2adds across the double bond.

Chemistry 140 Fall 2002 Naming the Stereoisomers of Highly Substituted Alkenes: The E,Z System of Nomenclature

26-6 Aromatic Hydrocarbons Kekulé structures Simplified molecular orbital representation Toluene o-Xylene Napthalene Anthracene

Characteristics of Aromatic Hydrocarbons Planar (flat) cyclic molecules. Conjugated п systems (4n + 2) August Kekulé (1829-1896) who proposed the hexagonal ring structure for benzene in 1865. His representation of this molecule is still widely used.

Naming Aromatic Hydrocarbons

26-7 Organic Compounds Containing Functional Groups Chemistry 140 Fall 2002 26-7 Organic Compounds Containing Functional Groups Alcohols and Phenols

Preparation and Use of Alcohols

Ethers Preparation and Uses of Ethers Chemistry 140 Fall 2002 Ethers Preparation and Uses of Ethers conc. H2SO4 CH3CH2OH + HOCH2CH3 CH3CH2OCH2CH3 + H2O 140°C

Aldehydes and Ketones carbonyl group Chemistry 140 Fall 2002 The carbonyl group

3-chloro-2-methylbutanal 4-chloro-3-methylpentan-2-one

Preparation and Uses of Aldehydes and Ketones Oxidation of alcohols. (26.13) ethanol (a primary alcohol) acetaldehyde (an aldehyde) acetic acid (an acid) (26.14) propane-2-ol (an secondary alcohol) acetone (a ketone)

Extract from natural sources

Reduction to alcohol

Carboxylic Acids carboxyl group

Preparation and Uses of Carboxylic Acids (26.16) (26.17)

Esters The distinctive aroma and flavor of oranges are due in part to the ester octyl acetate, CH3CO2CH2(CH2)6CH3

Amides

Resonance in an amide.

Preparation and Uses of Amides

Amines

Morphine , a very powerful and addictive painkiller, can be isolated from the opium poppy (Papaver somniferum).

Amines are weak bases

Quaternary ammonium ions

Heterocyclic Compounds Chemistry 140 Fall 2002 Heterocyclic Compounds FIGURE 26-17 Pyridine

26-8 From Molecular Formula to Molecular Structure C5H10 If an organic molecule with n carbon atoms has fewer than 2n+2 hydrogen atoms, then it contains elements of unsaturation, such as π bonds or ring structures

Alcohol Ether Ketone (or aldehyde)

C3H6O C3H8O C3H6O2

End of Chapter