Chemistry 102 - Review Sheet for Exam #2

Be familiar with the concepts below.  For nomenclature review information, go to Chem102 Exam #1 Review Sheet.

Chapter 15: Carbohydrates

Classes of Carbohydrates: Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield such compounds upon hydrolysis carbohydrates can exist either as single units (monosaccharides) or joined together in molecules ranging from two units (disaccharides) to hundreds of units (polysaccharides).

Stereochemistry of Carbohydrates: Carbohydrates, along with many other natural substances, exhibit a type of isomerism in which two isomers are mirror images of each other The two isomers are called enantiomers When a molecules has more than one chiral carbon, the maximum number of stereoisomers possible equals 2n where n is the number of chiral carbons.

Fischer Projections: A useful way of depicting the structure of chiral molecules employs crossed lines (Fischer projection) to represent chiral carbon atoms The prefixes D- and L- are used to distinguish between enantiomers signs indicating the rotation of plane-polarized light to the right (+) or to the left (-) may also be used to designate .enantiomers

Monosaccharides: Monosaccharides that contain an aldehyde group are called aldoses, whereas those containing a ketone group are ketoses Monosaccharides are also classified by the number of carbon atoms as trioses, tetroses, etc Most natural monosaccharides belong to the D-family.

Physical Properties of Monosaccharides: Monosaccharides are sweet-tasting solids that are very soluble in water noncarbohydrate low-calorie sweeteners such as aspartame have been developed as sugar substitutes.

Chemical Properties of Monosaccharides: Pentoses and hexoses form cyclic hemiacetals or hemiketals whose structures can be represented by Haworth structures Two isomers referred to as anomers are produced in the cyclization reaction All monosaccharides are oxidized by Benedict's or Fehling's reagent and are called reducing sugars Monosaccharides can react with alcohols to produce acetals or ketals that are called glycosides.

Important Monosaccharides: Ribose and deoxyribose are important as components of nucleic acids The hexoses glucose, galactose, and fructose are the most important nutritionally and the most abundant in nature Glucose, also known as blood sugar, is transported within the bloodstream to body tissues where it supplies energy.

Disaccharides: Glycosidic linkages join monosaccharide units together to form disaccharides Three important disaccharides are maltose (two glucose units linked together), lactose (a galactose linked to a glucose), and sucrose (glucose joined to fructose).

Polysaccharides: Cellulose, starch, and glycogen are three important polysaccharides Starch is the major storage form of glucose in plants, whereas glycogen is the storage form of glucose in animals Cellulose is the structural material of plants.

Chapter 16: Carboxylic Acids and Esters

Nomenclature of Carboxylic Acids: The characteristic functional group of carboxylic acids is the carboxyl group Many of the simpler carboxylic acids are well known by common names In the IUPAC system, the ending -oic acid is used in the names of these compounds Aromatic acids are named as derivatives of benzoic acid.

Physical Properties of Carboxylic Acids: At room temperature, low molecular weight carboxylic acids are liquids with distinctic sharp or unpleasant odors High molecular weight, long chain acids are wax-like solids carboxylic acids are quite effective in forming dimers in which two molecules are held together by hydrogen bonds Thus, they have relatively high boiling points, and those with lower molecular weights are soluble in water.

The Acidity of Carboxylic Acids: Soluble carboxylic acids behave as weak acids; they dissociate only slightly in water to form an equilibrium mixture with the carboxylate ion The equilibrium concentrations of the carboxylic acid and the carboxylate ion depend upon pH At low pH the acid form predominates, and at pH 74 (the pH of cellular fluids) and above, the carboxylate ion predominates carboxylic acids react with bases to produce carboxylate salts and water.

Salts of Carboxylic Acids: The carboxylate salts are named by changing the -ic ending of the acid to -ate The ionic nature of the salts makes them water soluble A number of carboxylate salts are useful as food preservatives, soaps, and medicines.

Carboxylic Esters: carboxylic acids, acid chlorides, and acid anhydrides react with alcohols to produce esters Polyesters result from the reaction of dicarboxylic acids and diols Polyesters are an example of condensation polymers; these are produced when monomers react to form a polymer plus a small molecule such as water.

Nomenclature of Esters: Both common and lUPAC names for esters are formed by first naming the alkyl group of the alcohol portion followed by the name of the acid portion in which the -ic acid ending has been changed to -ate Many esters are very fragrant and represent some of nature's most pleasant odors Because of this characteristic, esters are widely used as flavoring agents.

Reactions of Esters: Esters can be converted back to carboxylic acids and alcohols under either acidic or basic conditions Hydrolysis, the reaction with water in the presence of acid, produces the carboxylic acid and alcohol Saponification occurs in the presence of a base to produce the carboxylate salt and alcohol.

Esters of Inorganic Acids: Alcohols can also form esters by reaction with inorganic acids such as phosphoric acid Phosphate esters represent some of the most important biological compounds.