Chapter 24 Organic Chemistry

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.

Structure of Organic Molecules There are three hybridization states and geometries found in organic compounds: sp3 Tetrahedral sp2 Trigonal planar sp Linear

Hydrocarbons Hydrocarbons – compounds composed only of carbon and hydrogen There are four basic types of hydrocarbons: Alkanes Alkenes Alkynes Aromatic hydrocarbons

Alkanes Alkanes contain only single bonds. They are also known as saturated hydrocarbons. They are “saturated” with hydrogens.

Formulas Lewis structures of alkanes or structural formulas: Condensed formulas: General formula for noncyclic alkanes: CnH2n+2

First Ten Straight-Chain Alkanes and Their Physical Properties General formula: CnH2n+2

Structure of Alkanes Carbons in alkanes are sp3 hybrids. They have a tetrahedral geometry and 109.5° bond angles.

Structure of Alkanes There are only  - bonds in alkanes. There is free rotation about the C—C bonds.

Structural Isomers Structural isomers have the same molecular formulas, but the atoms are bonded in a different order. C4H10 C5H12 Two structural isomers for C4H10 Three structural isomers for C5H12 In general, the number of structural isomers increase as the number of carbons in the hydrocarbon increase.

Organic Nomenclature For straight-chain alkanes: base + suffix IUPAC - International Union of Pure and Applied Chemistry base – number of carbons suffix – type of compounds

Organic Nomenclature IUPAC names There are three parts to a compound name: Base: This tells how many carbons are in the longest continuous chain. Base Name # of C Atoms meth- 1 eth- 2 prop- 3 but- 4 pent- 5 hex- 6 hept- 7 oct- 8 non- 9 dec- 10 IUPAC - International Union of Pure and Applied Chemistry

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. alkane: -ane; alkene: -ene; alkyne: -yne

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.

How to Name a Compound Find the longest chain in the molecule. Number the chain from the end nearest the first substituent encountered. List the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached.

How to Name a Compound CH3 – CHCH3 CH2 – CH2 – CH2 – CH3 Find the longest chain in the molecule. Number the chain from the end nearest the first substituent encountered. List the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached. 2-Methyl hexane 16

How to Name a Compound If there is more than one type of substituent in the molecule, list them alphabetically. CH3 CH3 – CH – CH2 CH – CH – CH2 – CH3 CH3 CH – CH3 3-Ethyl-2,4,5-trimethyl heptane

Examples 1. Draw structure of heptane 2. Draw structure of 5-isopropyl-2-methyloctane. 3. Name the compound CH3CHCH2CHCH3 CH3 CH2CH3

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.

Alkenes Alkenes contain at least one carbon–carbon double bond. They are unsaturated. That is, they have fewer than the maximum number of hydrogens.

Structure of Alkenes Unlike alkanes, alkenes cannot rotate freely about the double bond. The side-to-side overlap in the -bond makes this impossible without breaking the -bond.

Geometric Isomers This creates geometric isomers, which differ from each other in the spatial arrangement of groups about the double bond.

Nomenclature of Alkenes Suffix: -ene Indicate position of double bond using a number. 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.

Alkenes Example Draw structure of 2-methyl-2-pentene. Draw all structural and geometric isomers of butene, C4H8, that have an unbranched hydrocarbon chain, and name them.

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.

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.

Aromatic Hydrocarbons Aromatic hydrocarbons are cyclic hydrocarbons that have some particular features. There is a p-orbital on each atom, forming -bonds. The molecule is planar. The -electrons are delocalized; this stabilizes aromatic compounds. There is an odd number of electron pairs in the -system. In aromatic compounds, unlike in alkenes and alkynes, each pair of -electrons does not sit between two atoms. Rather, the electrons are delocalized; this stabilizes aromatic compounds.

Functional Groups The term functional group is used to refer to parts of organic molecules where reactions tend to occur.

Alcohols Alcohols contain one or more hydroxyl groups, -OH. ..

Ethers Ethers have two hydrocarbon groups bonded to one oxygen atom.

Carbonyl Compounds The carbonyl group is a carbon-oxygen double bond. Carbonyl compounds include many classes of compounds.

Aldehydes In an aldehyde, at least one hydrogen is attached to the carbonyl carbon.

Ketones In ketones, two carbons bond to the carbonyl carbon.

Carboxylic Acids Carboxylic acids have a hydroxyl group bonded to the carbonyl group. Carboxylic acids are weak acids.

Esters Esters are the compounds in which the H atom of a carboxylic acid is replaced by a carbon-containing group. They are found in many fruits and perfumes.

Amides Amides are the compounds in which the NR2 group (R is H or carbon-containing group) replacing the OH of a carboxylic acid.

Amines General formula: R3N, R is H or carbon-containing group Amines are organic bases. They generally have strong, unpleasant odors.

Chirality 2-bromopentane Carbons with four different groups attached to them are handed, or chiral. These are optical isomers, or stereoisomers. If one stereoisomer is “right-handed,” its enantiomer is “left-handed.”

Chirality Many pharmaceuticals are chiral. Often only one enantiomer is clinically active. (s)-ibuprofen