GOB Chemistry Study Guide: Organic, Biochemical, and General Chemistry Concepts

Organic Chemistry Reactions and Oxidation

Oxidation of Alcohols

Alcohols can undergo oxidation reactions to form different products depending on their structure. Complete oxidation typically converts alcohols to carboxylic acids or ketones.

• Primary alcohols are oxidized to carboxylic acids.

• Secondary alcohols are oxidized to ketones.

• Tertiary alcohols generally do not undergo oxidation under mild conditions.

• Example: Oxidation of cyclobutanol (secondary alcohol) yields cyclobutanone (a ketone).

General equation for oxidation of a primary alcohol:

$\ce{RCH2OH + 2[O] \rightarrow RCOOH + H2O}$

General equation for oxidation of a secondary alcohol:

$\ce{R2CHOH + [O] \rightarrow R2CO + H2O}$

Combustion of Hydrocarbons

Complete Combustion Reaction

Combustion of hydrocarbons is a chemical reaction with oxygen that produces carbon dioxide and water. The reaction must be balanced to reflect conservation of mass.

• General formula: $\ce{C_xH_y + O_2 \rightarrow CO_2 + H_2O}$

• Example: Complete combustion of 5-ethyl-2-methylheptane:

$\ce{C_{10}H_{22}(l) + 15 O_2(g) \rightarrow 10 CO_2(g) + 11 H_2O(g)}$

Additional info: The actual balanced equation may vary depending on the hydrocarbon structure.

Organic Reaction Types

Classification of Organic Reactions

Organic reactions are classified based on the changes occurring in the molecules:

• Addition: Atoms are added to a molecule, typically across a double or triple bond.

• Elimination: Atoms are removed from a molecule, often resulting in the formation of double or triple bonds.

• Substitution: One atom or group is replaced by another.

• Rearrangement: The structure of the molecule is reorganized without adding or removing atoms.

• Example: Reaction of an alkyl halide with NaI is a substitution reaction.

Homogeneous and Heterogeneous Equilibria

Equilibrium Types

Chemical equilibria can be classified as homogeneous or heterogeneous:

• Homogeneous equilibrium: All reactants and products are in the same phase (e.g., all gases or all aqueous).

• Heterogeneous equilibrium: Reactants and products are in different phases (e.g., solids and gases).

• Example: $\ce{CaCO3(s) \rightleftharpoons CaO(s) + CO2(g)}$ is a heterogeneous equilibrium.

Solubility of Ionic Compounds

Solubility Rules

Solubility of ionic compounds in water depends on the ions present:

• Soluble compounds: Most nitrates, chlorates, and salts of alkali metals are soluble.

• Insoluble compounds: Most carbonates, hydroxides, and bromides (except those of alkali metals and ammonium) are insoluble.

• Example: Magnesium chlorate and lead(II) nitrate are soluble; barium carbonate and silver bromide are insoluble.

Chemical Equilibrium Expressions

Equilibrium Constant ($K_c$)

The equilibrium constant expresses the ratio of concentrations of products to reactants at equilibrium.

• General form: $K_c = \frac{[\text{products}]}{[\text{reactants}]}$

• Example: For $\ce{CaCO3(s) \rightleftharpoons CaO(s) + CO2(g)}$:

$K_c = [CO_2]$ (since solids are omitted from the expression)

Oxidation and Reduction

Redox Reactions

Oxidation involves the loss of electrons or increase in oxidation state; reduction involves gain of electrons or decrease in oxidation state.

• Example: Conversion of benzaldehyde ($\ce{C_6H_5CHO}$) to benzoic acid ($\ce{C_6H_5COOH}$) is an oxidation (aldehyde to carboxylic acid).

Carbohydrate Chemistry

Enzymatic Hydrolysis of Lactose

Lactose, a disaccharide, is hydrolyzed by the enzyme lactase into glucose and galactose, both monosaccharides.

• Equation: $\text{Lactose (disaccharide)} + \text{Lactase} \rightarrow \text{Glucose (monosaccharide)} + \text{Galactose (monosaccharide)}$

Acetal and Hemiacetal Linkages in Carbohydrates

Carbohydrates can form acetal and hemiacetal linkages:

• Hemiacetal linkage: Formed when an alcohol reacts with an aldehyde or ketone; present at the anomeric carbon of monosaccharides.

• Acetal linkage: Formed when a hemiacetal reacts with another alcohol; present in glycosidic bonds between sugars.

• Example: In a trisaccharide, linkage A may be acetal, B hemiacetal, and C acetal.

Enantiomers of Sugars

Enantiomers are mirror-image isomers. D- and L- sugars differ in the configuration at the chiral carbon furthest from the carbonyl group.

• Example: D-ribose and L-ribose are enantiomers.

• Structure: The arrangement of hydroxyl groups determines D- or L- form.

Polysaccharide Structure and Function

Starch vs. Glycogen

Starch and glycogen are both glucose polymers but differ in structure and biological role.

• Starch: Found in plants; consists of amylose (linear) and amylopectin (branched, branches every 20-30 units).

• Glycogen: Found in animals; highly branched (branches every 8-12 units).

• Bond types: Starch has α-1,4 and α-1,6 glycosidic bonds; glycogen has both, but more frequent branching.

• Function: Starch is energy storage in plants; glycogen is energy storage in animals.

Fatty Acids and Melting Points

Melting Point Comparison

The melting point of fatty acids depends on the presence of double bonds:

• Saturated fatty acids (e.g., palmitic acid) have higher melting points due to tight packing.

• Unsaturated fatty acids (e.g., oleic acid) have lower melting points because double bonds introduce kinks, preventing tight packing.

• Example: Palmitic acid has a higher melting point than oleic acid.

Thermodynamics: Heat and Work

Sign Conventions for q and w

In thermodynamics, q represents heat and w represents work:

• q > 0: System gains heat.

• q < 0: System loses heat.

• w > 0: Work is done on the system.

• w < 0: Work is done by the system.

• Example: If a system does work on the surroundings and loses heat, q < 0, w < 0.

Lipid Chemistry

Hydrolysis of Sphingomyelin

Sphingomyelin is a type of phospholipid. Base-catalyzed hydrolysis breaks it into its component parts:

• Products: Ceramide, phosphocholine, and fatty acid.

• General reaction: Sphingomyelin + base → ceramide + phosphocholine + fatty acid

Nutrition and Energy Values

Energy Content of Macronutrients

Carbohydrates and proteins provide 4 kcal/g, fats provide 9 kcal/g. Daily caloric intake is calculated based on these values.

• Example: A diet with 2000 kcal/day is needed to maintain weight for most adults.

• Calculation: Multiply grams of each macronutrient by its energy value and sum for total daily intake.

Solution Chemistry

Solvent and Solute Identification

In a solution, the solvent is the component present in the greatest amount, while the solute is present in lesser amounts.

• Example: In a mixture of 100 g sodium bicarbonate, 900 g sodium carbonate, and 10 kg water, water is the solvent.

Volume/Volume Percent Concentration

Volume percent concentration expresses the amount of solute in a given volume of solution.

• Formula: $\text{Volume percent} = \frac{\text{Volume of solute}}{\text{Volume of solution}} \times 100\%$

• Application: Used for solutions where both solute and solvent are liquids.