Acids, Bases, and Organic Nomenclature: Study Notes for Introductory Chemistry

Acids and Bases

Definitions and Key Concepts

Acids and bases are fundamental chemical species that participate in proton transfer reactions. Understanding their properties and behavior is essential for studying chemical reactions and solution chemistry.

• Acid: A molecule that donates a hydrogen ion (H+).

• Base: A molecule that accepts a hydrogen ion (H+).

• Conjugate Pair: Two molecules that differ only by the presence or absence of one H+ ion.

• Example: Water (H2O) can lose a hydrogen ion to become hydroxide (OH-). These two form a conjugate acid-base pair.

The pH Scale and Calculations

The pH scale quantifies the acidity or basicity of a solution, ranging from 0 (most acidic) to 14 (most basic).

• Low pH (0-6): Acidic solution (high concentration of H+ ions).

• pH 7: Neutral solution (pure water).

• High pH (8-14): Basic solution (high concentration of OH- ions).

• Balance: In water, H+ and OH- concentrations are inversely related; as one increases, the other decreases.

Formula: The pH is calculated as:

$pH = -\log_{10}[H^+]$

Additional info: The concentration of hydrogen ions, [H+], is measured in moles per liter (M).

Titration

Titration is a laboratory technique used to determine the concentration of an unknown acid or base by reacting it with a base or acid of known concentration until neutralization occurs.

• Neutralization: Occurs when acid and base react in stoichiometric proportions, typically forming water and a salt.

• Key Formula: For a 1:1 reaction ratio:

$M_1V_1 = M_2V_2$

• Where M1 and V1 are the molarity and volume of the acid, and M2 and V2 are those of the base.

Example: If 0.1 M HCl neutralizes 25 mL of NaOH, the concentration of NaOH can be found using the formula above.

Organic Chemistry: Naming and Structure

Naming Carbon Chains (Alkanes, Alkenes, Alkynes)

Organic compounds are named systematically based on the length and structure of their carbon chains and the presence of functional groups or multiple bonds.

• Step 1: Identify the longest continuous chain of carbon atoms (the parent chain).

• Step 2: Number the chain from the end nearest a branch or multiple bond.

• Step 3: Name and number branches (substituents) according to their size and position.

Example: A three-carbon chain is called propane; a four-carbon chain is butane.

Prefixes for Number of Carbons

Number of Carbons	Prefix
1	Meth-
2	Eth-
3	Prop-
4	But-
5	Pent-
6	Hex-
7	Hept-
8	Oct-
9	Non-
10	Dec-

Standard Steps for Naming Saturated Alkanes (Single Bonds)

• Principal Chain: Longest continuous chain of carbon atoms determines the parent name.

• Numbering: Number the chain from the end that gives substituents the lowest possible numbers.

• Substituents: Groups attached to the chain are named as alkyl groups (suffix -yl).

• Assembly: Combine locant numbers, substituent names, and parent chain (e.g., 4-methylheptane).

Example: A methyl group (–CH3) on the fourth carbon of heptane is named 4-methylheptane.

Naming Unsaturated Hydrocarbons (Alkenes & Alkynes)

• Alkenes: Contain at least one double bond; parent name ends in -ene.

• Alkynes: Contain at least one triple bond; parent name ends in -yne.

• Numbering: The chain is numbered to give the multiple bond the lowest possible number, even if this overrides substituent positions.

Example: A four-carbon chain with a triple bond at the end is named 1-butyne.

Functional Groups and Their Naming

Functional groups are specific groups of atoms that impart characteristic chemical properties to organic molecules.

• Alcohols: Contain a hydroxyl group (–OH) attached to a saturated carbon. Suffix changes to -ol, with locant number (e.g., 2-propanol).

• Ethers: Have an oxygen atom between two alkyl groups (R–O–R'). Name each alkyl group and add 'ether' (e.g., ethyl butyl ether).

• Aldehydes: Have a terminal carbonyl group (–CHO). Suffix changes to -al; no locant needed (e.g., butanal).

Common Alkyl Groups: Condensed Structural Formulas

Condensed Structural Formula	Name
$-CH_3$	methyl
$CH_2CH_3$	ethyl
$CH_2CH_2CH_3$	propyl
$CH_2CH_2CH_2CH_3$	butyl
$\begin{array}{c} CH \\ | \\ CH_3 \end{array}$	isopropyl
$\begin{array}{c} CH_2CH \\ | \\ CH_3 \end{array}$	isobutyl
$\begin{array}{c} CHCH_2CH_3 \\ | \\ CH_3 \end{array}$	sec-butyl
$\begin{array}{c} CH_3 \\ | \\ CCH_3 \\ | \\ CH_3 \end{array}$	tert-butyl

Summary Table: Functional Groups

Functional Group	Structure	Naming Suffix	Example Name
Alcohol	–OH	-ol	2-propanol
Ether	R–O–R'	ether	ethyl butyl ether
Aldehyde	–CHO	-al	butanal

Additional info: The systematic naming of organic compounds is governed by IUPAC rules, which ensure that each compound has a unique and descriptive name. Mastery of these conventions is essential for clear communication in chemistry.