Acids and Bases

Definitions and Properties

Acids and bases are fundamental classes of compounds in chemistry, each with distinct properties and definitions according to different theories.

• Acids are substances that donate a hydrogen ion (H+), according to both the Arrhenius and Brønsted-Lowry definitions.

• Bases are substances that either donate hydroxide ions (OH-) (Arrhenius) or accept hydrogen ions (Brønsted-Lowry).

• Common acids: HCl, H2SO4, HNO3, HC2H3O2

• Common bases: NaOH, KOH, Ca(OH)2, Ba(OH)2

Conjugate Acid-Base Pairs

• When an acid donates an H+, it forms its conjugate base.

• When a base accepts an H+, it forms its conjugate acid.

• These pairs differ by one proton (H+).

Neutralization Reactions

When an acid reacts with a base, a neutralization reaction occurs, producing a salt and water.

• General equation:

pH Scale

• The pH scale measures the acidity or basicity of a solution.

• pH = 7: Neutral

• pH < 7: Acidic

• pH > 7: Basic

• Stronger acids have lower pH values; stronger bases have higher pH values.

Introduction to Organic Chemistry: Hydrocarbons

General Properties of Organic Compounds

• Organic compounds are primarily composed of carbon and hydrogen.

• They are generally nonpolar, insoluble in water, less dense than water, and flammable.

Alkanes

• Alkanes are saturated hydrocarbons with only single bonds.

• General formula:

• Examples: methane, ethane, propane, ... decane.

Structural Formulas

• Molecular formula: Shows the number of each type of atom (e.g., C2H6).

• Expanded structural formula: Shows all bonds between atoms.

• Condensed structural formula: Groups atoms together (e.g., CH3CH3).

• Line-angle formula: Uses lines to represent carbon chains.

Cycloalkanes

• Cycloalkanes are ring-shaped saturated hydrocarbons.

• General formula:

• Examples: cyclopropane, cyclobutane, etc.

Structural Isomers

• Isomers have the same molecular formula but different structures and properties.

• Alkanes, alkenes, and cycloalkanes can be structural isomers (e.g., butene and cyclobutene).

Properties of Alkanes: Combustion

• Alkanes undergo combustion to produce carbon dioxide and water.

• General equation:

Example: Combustion of methane:

Alkenes

• Alkenes are unsaturated hydrocarbons with at least one double bond.

• General formula:

• Examples: ethene, propene, butene, etc.

Geometric (cis-trans) Isomers

• Alkenes can have cis (same side) and trans (opposite side) isomers due to restricted rotation around the double bond.

Alkynes

• Alkynes are unsaturated hydrocarbons with at least one triple bond.

• General formula:

• Examples: ethyne, propyne, butyne, etc.

Hydrogenation Reaction

• Alkenes and alkynes can be converted to alkanes by adding hydrogen (H2) in the presence of a catalyst (Pt, Pd, or Ni).

Aromatic Compounds: Benzene

• Benzene is a planar, cyclic aromatic hydrocarbon with the formula C6H6.

• Its structure is often represented as a hexagon with a circle inside, indicating delocalized electrons.

Survey of Functional Groups

Common Functional Groups

Functional groups are specific groups of atoms within molecules that determine the chemical properties of those molecules.

The Carbonyl Group

• The carbonyl group consists of a carbon atom double-bonded to an oxygen atom (C=O).

• The carbon atom in this group is called the carbonyl carbon.

Esterification

• Esterification is the reaction of an alcohol with a carboxylic acid to form an ester and water.

• General equation:

• Mechanism: Remove OH from the acid and H from the alcohol.

• Be able to predict products from reactants and vice versa.

Amidation

• Amidation is the reaction of an amine with a carboxylic acid to form an amide and water.

• General equation:

• Mechanism: Remove OH from the acid and H from the amine.

• Be able to predict products from reactants and vice versa.

Carbohydrates (Up to Monosaccharides)

Types of Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).

• Disaccharides: Two monosaccharides joined together (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharide units (e.g., starch, cellulose, glycogen).

Stereoisomers / Optical Isomers / Enantiomers

• Stereoisomers are compounds with the same molecular formula and connectivity but different spatial arrangements.

• Chiral carbon: A carbon atom bonded to four different groups.

• If a molecule has a chiral carbon, it is chiral and can exist as two enantiomers (non-superimposable mirror images).

• Enantiomers have different biological properties.

Classification of Monosaccharides

• By number of carbons: triose (3C), tetrose (4C), pentose (5C), hexose (6C), etc.

• By carbonyl group:

  • Aldose: Contains an aldehyde group (-CHO).

  • Ketose: Contains a ketone group (C=O within the chain).

• Combined classification: e.g., aldotriose, ketotetrose.

D and L Enantiomers of Monosaccharides

• Monosaccharides can exist as D- or L- enantiomers, based on the configuration around the chiral carbon farthest from the carbonyl group.

• Only D-enantiomers are commonly found in nature.

Haworth Projections: α and β Anomers

• Monosaccharides can cyclize to form ring structures, represented by Haworth projections.

• The anomeric carbon is the carbon derived from the carbonyl group during ring formation.

• α and β anomers differ in the position of the OH group on the anomeric carbon.

• If one of the oxygens on the anomeric carbon is attached to a hydrogen, the anomeric carbon is considered "free".

Three Important Monosaccharides