Chapter 24 Organic Chemistry © 2012 Pearson Education, Inc.

© 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 © 2012 Pearson Education, Inc.

What is the geometry around the bottom carbon atom in acetonitrile? A. Octahedral B. Trigonal planar C. Linear D. Tetrahedral Answer: D

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. © 2012 Pearson Education, Inc.

C-H C-C C=N C-H and C-C Answer: C

Polar Solvents Nonpolar Solvents Change in solubility: Polar Solvents Nonpolar Solvents A.Increase Increase B.Increase Decrease C.Decrease Increase D.Decrease Decrease Answer: C

© 2012 Pearson Education, Inc. Hydrocarbons There are four basic types of hydrocarbons: Alkanes Alkenes Alkynes Aromatic hydrocarbons © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Alkanes Alkanes contain only single bonds. They are also known as saturated hydrocarbons. They are “saturated” with hydrogens. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. 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. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Properties of Alkanes The only van der Waals force is the London dispersion force. The boiling point increases with the length of the chain. © 2012 Pearson Education, Inc.

Two C-H bonds and one C-C bond Two C-H bonds and two C-C bonds Three C-H bonds and one C-C bond Four C-H bonds and two C-C bonds Answer: B

© 2012 Pearson Education, Inc. Structure of Alkanes Carbons in alkanes are sp3 hybrids. They have a tetrahedral geometry and 109.5 bond angles. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Structure of Alkanes There are only -bonds in alkanes. There is free rotation about the C—C bonds. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Isomers Isomers have the same molecular formulas, but the atoms are bonded in a different order. © 2012 Pearson Education, Inc.

Lewis structures of isomers are different and this proves that isomers have different physical and chemical properties. Each isomer of a hydrocarbon molecule has a different number of C-H bonds and therefore the isomers have different physical and chemical properties. Melting and boiling points can be significantly different as shown in Table 24.3 of text. All of the above Answer: C

© 2012 Pearson Education, 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. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. 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. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. How to Name a Compound If there is more than one type of substituent in the molecule, list them alphabetically. © 2012 Pearson Education, Inc.

Sample Exercise 24.1 Naming Alkanes Give the systematic name for the following alkane: Practice Exercise Name the following alkane:

Sample Exercise 24.2 Writing Condensed Structural Formulas Write the condensed structural formula for 3-ethyl-2-methylpentane. Practice Exercise Write the condensed structural formula for 2,3-dimethylhexane. 21

© 2012 Pearson Education, 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. © 2012 Pearson Education, Inc.

A. CnH2n–2 B. CnH2n–1 C. CnH2n D. CnH2n+1 Answer: C

© 2012 Pearson Education, 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. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. 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. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Structure of Alkenes This creates geometric isomers, which differ from each other in the spatial arrangement of groups about the double bond. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Structure of Alkenes Structure also affects the physical properties of alkenes. © 2012 Pearson Education, Inc.

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

One Two Three Four Answer: B

Practice Exercise Sample Exercise 24.3 Drawing Isomers Draw all the structural and geometric isomers of pentene, C5H10, that have an unbranched hydrocarbon chain. Practice Exercise How many straight-chain isomers are there of hexene, C6H12? 30

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. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, 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. © 2012 Pearson Education, 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. © 2012 Pearson Education, Inc.

Practice Exercise Sample Exercise 24.4 Naming Unsaturated Hydrocarbons Name the following compounds: Practice Exercise Draw the condensed structural formula for 4-methyl-2-pentyne. 34

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. © 2012 Pearson Education, Inc.

Aromatic Nomenclature Many aromatic hydrocarbons are known by their common names. © 2012 Pearson Education, 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. para-: On opposite sides of ring. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Functional Groups The term functional group is used to refer to parts of organic molecules where reactions tend to occur. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, 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. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Alcohols Alcohols are much more acidic than hydrocarbons. pKa ~15 for most alcohols. Aromatic alcohols have pKa ~10. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Ethers Ethers tend to be quite unreactive. Therefore, they are good polar solvents. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Aldehydes In an aldehyde, at least one hydrogen is attached to the carbonyl carbon. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Ketones In ketones, there are two carbons bonded to the carbonyl carbon. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Carboxylic Acids Acids have a hydroxyl group bonded to the carbonyl group. They are tart tasting. Carboxylic acids are weak acids. © 2012 Pearson Education, Inc.

A. Lactic acid and formic acid B. Citric acid and ethanoic acid C. Ethanoic acid and benzoic acid D. Lactic acid and citric acid Answer: D

© 2012 Pearson Education, Inc. Esters Esters are the products of reactions between carboxylic acids and alcohols. They are found in many fruits and perfumes. © 2012 Pearson Education, Inc.

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 Exercise Write the condensed structural formula for the ester formed from propyl alcohol and propionic acid. 47

A. Presence of C-O-C bond. B. Long hydrocarbon chains C. Presence of ester linkage D. Presence of C=O group Answer: B

Answer: C 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.

© 2012 Pearson Education, Inc. Amides Amides are formed by the reaction of carboxylic acids with amines. © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Amines Amines are organic bases. They generally have strong, unpleasant odors. © 2012 Pearson Education, Inc.