Chapter 25 Organic and Biological Chemistry

Chapter 25 Organic and Biological Chemistry

Chemistry, The Central Science, 11th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chapter 25 Organic and Biological Chemistry John D. Bookstaver Organic and Biological St. Charles Community College Chemistry Cottleville, MO © 2009, Prentice-Hall, Inc. Organic Chemistry • Organic chemistry is the chemistry of carbon compounds. • Carbon has the ability to form long chains. • Without this property, large biomolecules such as proteins, lipids, carbohydrates, and nucleic acids could not form. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Carbon Compounds • There are three hybridization states and geometries found in organic compounds: – sp3 Tetrahedral – sp2 Trigonal planar – sp Linear Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Hydrocarbons • There are four basic types of hydrocarbons: – Alkanes – Alkenes – Alkynes – Aromatic hydrocarbons Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alkanes • Alkanes contain only single bonds. • They are also known as saturated hydrocarbons. – They are “saturated” with hydrogens. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Formulas • Lewis structures of alkanes look like this. • They are also called structural formulas. • They are often not convenient, though… Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Formulas …so more often condensed formulas are used. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Properties of Alkanes • The only van der Waals force is the London dispersion force. Organic and • The boiling point increases with the length Biological of the chain. Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkanes • Carbons in alkanes are sp3 hybrids. • They have a tetrahedral geometry and 109.5° bond angles. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkanes • There are only σ- bonds in alkanes. • There is free rotation about the C—C bonds. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Isomers Isomers have the same molecular formulas, but the atoms are bonded in a different order. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Organic Nomenclature • There are three parts to a compound name: – Base: This tells how many carbons are in the longest continuous chain. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Organic Nomenclature • There are three parts to a compound name: – Base: This tells how many carbons are in the longest continuous chain. – Suffix: This tells what type of compound it is. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Organic Nomenclature • There are three parts to a compound name: – Base: This tells how many carbons are in the longest continuous chain. – Suffix: This tells what type of compound it is. – Prefix: This tells what groups are attached to the chain. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. How to Name a Compound 1. Find the longest chain in the molecule. 2. Number the chain from the end nearest the first substituent encountered. 3. List the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. How to Name a Compound If there is more than one type of substituent in the molecule, list them alphabetically. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Cycloalkanes • Carbon can also form ringed structures. • Five- and six-membered rings are most stable. – They can take on conformations in which their bond angles are very close to the tetrahedral angle. – Smaller rings are quite strained. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Alkanes • Alkanes are rather unreactive due to the presence of only C—C and C—H σ-bonds. • Therefore, they make great nonpolar solvents. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alkenes • Alkenes contain at least one carbon–carbon double bond. • They are unsaturated. – That is, they have fewer than the maximum number of hydrogens. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkenes • Unlike alkanes, alkenes cannot rotate freely about the double bond. – The side-to-side overlap in the π-bond makes this impossible without breaking the π-bond. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Alkenes This creates geometric isomers, which differ from each other in the spatial arrangement of groups about the double bond. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Properties of Alkenes Structure also affects the physical properties of alkenes. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Nomenclature of Alkenes • The chain is numbered so the double bond gets the smallest possible number. • cis-Alkenes have the carbons in the chain on the same side of the molecule. • trans-Alkenes have the carbons in the chain on opposite sides of the molecule. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Alkenes • One reaction of alkenes is the addition reaction. – In it, two atoms (e.g., bromine) add across the double bond. – One π-bond and one σ-bond are replaced by two σ-bonds; therefore, ΔH is negative. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Mechanism of Addition Reactions • It is a two-step mechanism: – The first step is the slow, rate-determining step. – The second step is fast. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Mechanism of Addition Reactions In the first step, the π-bond breaks and the new C—H bond and a cation form. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Mechanism of Addition Reactions In the second step, a new bond forms between the negative bromide ion and the positive carbon. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alkynes • Alkynes contain at least one carbon–carbon triple bond. • The carbons in the triple bond are sp-hybridized and have a linear geometry. • They are also unsaturated. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Nomenclature of Alkynes 4-methyl-2-pentyne • The method for naming alkynes is analogous to the naming of alkenes. • However, the suffix is -yne rather than -ene. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Alkynes • Alkynes undergo many of the same reactions alkenes do. • As with alkenes, the impetus for reaction is the replacement of π-bonds with σ-bonds. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Aromatic Hydrocarbons • Aromatic hydrocarbons are cyclic hydrocarbons that have some particular features. • There is a p-orbital on each atom. – The molecule is planar. • There is an odd number of electron pairs in the - π Organic and system. Biological Chemistry © 2009, Prentice-Hall, Inc. Aromatic Nomenclature Many aromatic hydrocarbons are known by their common names. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Aromatic Compounds • In aromatic compounds, unlike in alkenes and alkynes, each pair of π-electrons does not sit between two atoms. • Rather, the electrons are delocalized; this stabilizes aromatic compounds. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Aromatic Compounds • Due to this stabilization, aromatic compounds do not undergo addition reactions; they undergo substitution. • In substitution reactions, hydrogen is replaced by a substituent. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Structure of Aromatic Compounds • Two substituents on a benzene ring could have three possible relationships: – ortho-: On adjacent carbons. – meta-: With one carbon between them. Organic and – para-: On opposite sides of ring. Biological Chemistry © 2009, Prentice-Hall, Inc. Reactions of Aromatic Compounds Halogenation Friedel-Crafts Reaction Reactions of aromatic compounds often require a catalyst. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Functional Groups The term functional group is used to refer to parts of organic molecules where reactions tend to occur. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alcohols • Alcohols contain one or more hydroxyl groups, —OH. • They are named from the parent hydrocarbon; the suffix is changed to -ol and a number designates the carbon to which the hydroxyl is attached. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Alcohols • Alcohols are much more acidic than hydrocarbons. – pKa ~15 for most alcohols. – Aromatic alcohols have pKa ~10. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Ethers • Ethers tend to be quite unreactive. • Therefore, they are good polar solvents. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Carbonyl Compounds • The carbonyl group is a carbon-oxygen double bond. • Carbonyl compounds include many classes of compounds. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Aldehydes In an aldehyde, at least one hydrogen is attached to the carbonyl carbon. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Ketones In ketones, there are two carbons bonded to the carbonyl carbon. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Carboxylic Acids • Acids have a hydroxyl group bonded to the carbonyl group. • They are tart tasting. • Carboxylic acids are weak acids. Organic and Biological Chemistry © 2009, Prentice-Hall, Inc. Esters • Esters are the products of reactions between carboxylic acids and alcohols. • They are

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