25.1 Some General Characteristics of Organic Molecules25.1 Some General Characteristics of Organic Molecules

Organic chemistry is

The structures of organic moleculesThe structures of organic molecules

The shapes of organic and biochemical molecules are important in determining

their physical and chemical properties. Consider carbon:

The stabilities of organic substancesThe stabilities of organic substances

The stability of organic substances varies – e.g. benzene has special stability due

to the delocalization of ! electrons.

Chapter 25 The Chemistry of Life: Organic ChemistryChapter 25 The Chemistry of Life: Organic Chemistry

Solubility and acid-base properties of organicSolubility and acid-base properties of organic

substancessubstances

The prevalence of C-C and C-H bonds results

in low overall polarity for many organic molecules,

and such molecules are soluble in nonpolar

solvents.

25.2 Introduction to Hydrocarbons25.2 Introduction to Hydrocarbons

The simplest class of organic molecules is the hydrocarbons

25.3 25.3 AlkanesAlkanes

Single bonds only; “saturated” hydrocarbons (saturated with hydrogen).

Structures of Structures of AlkanesAlkanes

VSEPR theory predicts each

C atom is tetrahedral:

Structural IsomersStructural Isomers

In straight-chain hydrocarbons the C atoms are joined in a continuous chain.

Branched-chain hydrocarbons are possible for alkanes with four or more C atoms.

Structures with different branches can be written for the same formula:

Structural isomers are compounds with the same molecular formula but different

bonding arrangements.

Nomenclature of Nomenclature of AlkanesAlkanes

Organic compounds are named according to rules established by the International

Union for Pure and Applied Chemistry (IUPAC).

suffixbaseprefix

To name a compound…

2. Number the chain from the end

nearest the first substituent

encountered

4. When two or more substituents are

present, list them in alphabetical order.

CycloalkanesCycloalkanes

Carbon can also form ringed structures. 5- and 6-membered rings are most stable:

Reactions of Reactions of alkanesalkanes

Rather unreactive due to presence of only C–C and C–H "-bonds.

25.4 Unsaturated Hydrocarbons25.4 Unsaturated Hydrocarbons

AlkenesAlkenes

Alkenes are unsaturated hydrocarbons that contain C and H atoms and at least

one C-C double bond.

Alkenes are named in the same way as alkanes with the suffix -ene replacing the

-ane in alkanes. The location of the double bond is indicated by a prefix

Alkenes cannot rotate freely about the double bond (! bond = side-to-side overlap)

No rotation means

geometric isomers

are possible in alkenes

Structure affects physical properties of alkenes. Cis and trans do not interconvert.

AlkynesAlkynes

Unsaturated hydrocarbons that contain at least one carbon–carbon triple bond.

Naming is analogous to alkenes

Addition Reactions of Alkenes and AlkynesAddition Reactions of Alkenes and Alkynes

The dominant reactions for alkenes and alkynes are addition reactions:

Common additions include H2 (hydrogenation), H2O or hydrogen halides. Alkynes

are also capable of addition reactions:

Mechanism of Addition ReactionsMechanism of Addition Reactions

A mechanism is an explanation of how a reaction proceeds.

Aromatic HydrocarbonsAromatic Hydrocarbons

Aromatic structures are formally related to

benzene (C6H6):

Highly unsaturated: very reactive?

Even though they contain ! bonds, aromatic

hydrocarbons undergo substitution reactions

more readily than addition reactions.

25.5 Functional Groups: Alcohols and Ethers25.5 Functional Groups: Alcohols and Ethers

Hydrocarbons are relatively unreactive; for an organic molecule to be reactive it

needs something additional.

Alcohols, RAlcohols, R––OHOH

Named from parent hydrocarbon; suffix changed to -ol

The O–H bond is polar and can participate in hydrogen bonding, so alcohols are

more water soluble than alkanes.

Ethers, REthers, R––OO––RR’’

Compounds in which two hydrocarbons are linked by an oxygen are called ethers.

25.6 Compounds with a Carbonyl Group25.6 Compounds with a Carbonyl Group

The carbonyl group, C=O, plus the type of atoms attached to the carbonyl carbon

defines the particular kind of compound.

AldehydesAldehydes and and KetonesKetones

Aldehydes must have at least one H atom attached to the carbonyl C

Ketones have two carbons bonded to carbonyl carbon

Carboxylic AcidsCarboxylic Acids

Carboxylic acids contain a carbonyl group with an –OH attached

EstersEsters

Esters can be prepared by condensation reactions involving a

carboxylic acid and an alcohol; the products are the ester and water

Amines and amidesAmines and amides

Amines are organic bases with general formula R3N.

Amides are composites of carbonyl and amine functionalities

25.7 25.7 ChiralityChirality in Organic Chemistry in Organic Chemistry

Recall that molecules whose mirror images are nonsuperimposable are chiral.

Chemists use the labels R– and S– to distinguish between enantiomers.

Many pharmaceuticals are chiral; often only one enantiomer is clinically active.

A mixture of two enantiomers in the same quantity is called a racemic mixture.