Chapter 24 Organic Chemistry © 2012 Pearson Education, Inc

Chapter 24

Organic Chemistry

© 2012 Pearson Education, Inc.

Hydrocarbons

• Carbon has 4 valence electrons, and therefore forms 4 bonds.– 4 single bonds; tetrahedral; sp3 hybridized– 1 double and 2 single bonds; trigonal planar; sp2

hybridized– 1 triple and 1 single, or 2 double bonds; linear; sp

hybridized


What is the geometry around the bottom carbon atom in acetonitrile?

A. OctahedralB. Trigonal planarC. LinearD. Tetrahedral

Organic and Biological Chemistry

Stability of Organic Substances

• Carbon has an exceptional ability to bond to itself– C-H and C-C bond are non-polar– C-O and O-H bonds are very polar– Often the reactivity or other properties of an organic

molecule are determined by the presence of functional groups.



A. C-HB. C-CC. C=ND. C-H and C-C


Change in solubility:Polar Solvents Nonpolar Solvents

A.Increase IncreaseB.Increase DecreaseC.Decrease IncreaseD.Decrease Decrease


Hydrocarbons

• 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 look like this

• They are also called structural formulas.• They are often not convenient, though, so

more often condensed formulas are used.



Properties of Alkanes• The only van der Waals force is the London

dispersion force.• The boiling point increases with the length

of the chain.



A. Two C-H bonds and one C-C bondB. Two C-H bonds and two C-C bondsC. Three C-H bonds and one C-C bondD. Four C-H bonds and two C-C bonds


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.



IsomersIsomers have the same molecular formulas, but the atoms are bonded in a different order.



A. Lewis structures of isomers are different and this proves that isomers have different physical and chemical properties.

B. Each isomer of a hydrocarbon molecule has a different number of C-H bonds and therefore the isomers have different physical and chemical properties.

C. Melting and boiling points can be significantly different as shown in Table 24.3 of text.

D. All of the above


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

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.



How to Name a Compound

If there is more than one type of substituent in the molecule, list them alphabetically.



Sample Exercise 24.1 Naming Alkanes

Give the systematic name for the following alkane:

Practice ExerciseName the following alkane:


Sample Exercise 24.2 Writing Condensed Structural Formulas

Write the condensed structural formula for 3-ethyl-2-methylpentane.

Practice ExerciseWrite the condensed structural formula for 2,3-dimethylhexane.


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.



A. CnH2n–2

B. CnH2n–1

C. CnH2n

D. CnH2n+1


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.




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




Structure also affects the physical properties of alkenes.



A. 1B. 2C. 3D. 4


A. OneB. TwoC. ThreeD. Four


Sample Exercise 24.3 Drawing IsomersDraw all the structural and geometric isomers of pentene, C5H10, that have an unbranched hydrocarbon chain.

Practice ExerciseHow many straight-chain isomers are there of hexene, C6H12?


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.



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

• The method for naming alkynes is analogous to the naming of alkenes.

• However, the suffix is -yne rather than -ene.

4-methyl-2-pentyne



Sample Exercise 24.4 Naming Unsaturated Hydrocarbons

Name the following compounds:

Practice ExerciseDraw the condensed structural formula for 4-methyl-2-pentyne.


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 -system.



Aromatic Nomenclature

Many aromatic hydrocarbons are known by their common names.



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.– para-: On opposite sides of ring.



Functional GroupsThe 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.

• 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.



Alcohols• Alcohols are much more acidic than hydrocarbons.

– pKa ~15 for most alcohols.

– Aromatic alcohols have pKa ~10.



Ethers

• Ethers tend to be quite unreactive.• Therefore, they are good polar solvents.



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



Ketones

In ketones, there are two carbons bonded to the carbonyl carbon.



Carboxylic Acids

• Acids have a hydroxyl group bonded to the carbonyl group.

• They are tart tasting.• Carboxylic acids are weak acids.



A. Lactic acid and formic acidB. Citric acid and ethanoic acidC. Ethanoic acid and benzoic acidD. Lactic acid and citric acid


Esters

• Esters are the products of reactions between carboxylic acids and alcohols.

• They are found in many fruits and perfumes.



Sample Exercise 24.6 Naming Esters and Predicting Hydrolysis Products

In a basic aqueous solution, esters react with hydroxide ion to form the salt of the carboxylic acid and the alcohol from which the ester is constituted. Name each of the following esters, and indicate the products of their reaction with aqueous base.

Practice ExerciseWrite the condensed structural formula for the ester formed from propyl alcohol and propionic acid.


A. Presence of C-O-C bond.B. Long hydrocarbon chainsC. Presence of ester linkageD. Presence of C=O group


A. Solubility of phospholipids in water increases with greater size and mass of multiple layers.

B. Solubility of phospholipids in water increases with length of hydrophobic region.C. Hydrophobic tails (nonpolar) mutually interact with one another and hydrophilic

heads (polar) interact with water.D. Hydrophilic tails (nonpolar) mutually interact with one another and hydrophobic

heads (polar) interact with water.


Amides

Amides are formed by the reaction of carboxylic acids with amines.



Amines

• Amines are organic bases.• They generally have strong, unpleasant odors.


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Chapter 24 Organic Chemistry © 2012 Pearson Education, Inc