IB Chem SL: Organic Chemistry

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### Introduction to Organic Chemistry - **Definition:** Study of carbon compounds, primarily those containing C-H bonds. - **Key characteristics of Carbon:** - Forms 4 covalent bonds. - Can form single, double, and triple bonds. - Can bond with itself to form long chains, rings, and branched structures. - **Catenation:** Ability of carbon to form bonds with other carbon atoms. - **Hydrocarbons:** Compounds containing only carbon and hydrogen. ### Homologous Series - A series of organic compounds with the same general formula, usually varying by a single parameter such as the length of a carbon chain. - **Characteristics:** - Same general formula. - Gradation in physical properties (e.g., boiling point increases with chain length). - Similar chemical properties. - Successive members differ by a $-\text{CH}_2-$ unit. #### Common Homologous Series | Series | General Formula | Functional Group | Example (Name) | |-------------|-----------------|-------------------------|-----------------| | Alkanes | $\text{C}_n\text{H}_{2n+2}$ | C-C single bonds | $\text{CH}_4$ (Methane) | | Alkenes | $\text{C}_n\text{H}_{2n}$ | $\text{C}=\text{C}$ double bond | $\text{C}_2\text{H}_4$ (Ethene) | | Alkynes | $\text{C}_n\text{H}_{2n-2}$ | $\text{C}\equiv\text{C}$ triple bond | $\text{C}_2\text{H}_2$ (Ethyne) | | Halogenoalkanes | $\text{C}_n\text{H}_{2n+1}\text{X}$ | $-\text{X}$ ($\text{F, Cl, Br, I}$) | $\text{CH}_3\text{Cl}$ (Chloromethane) | | Alcohols | $\text{C}_n\text{H}_{2n+1}\text{OH}$ | $-\text{OH}$ (Hydroxyl) | $\text{CH}_3\text{OH}$ (Methanol) | | Aldehydes | $\text{C}_n\text{H}_{2n}\text{O}$ | $-\text{CHO}$ (Carbonyl at end) | $\text{HCHO}$ (Methanal) | | Ketones | $\text{C}_n\text{H}_{2n}\text{O}$ | $\text{C}=\text{O}$ (Carbonyl in middle) | $\text{CH}_3\text{COCH}_3$ (Propanone) | | Carboxylic Acids | $\text{C}_n\text{H}_{2n}\text{O}_2$ | $-\text{COOH}$ (Carboxyl) | $\text{HCOOH}$ (Methanoic acid) | | Esters | $\text{C}_n\text{H}_{2n}\text{O}_2$ | $-\text{COO}-$ (Ester linkage) | $\text{CH}_3\text{COOCH}_3$ (Methyl ethanoate) | ### Isomerism - **Definition:** Compounds with the same molecular formula but different structural formulas. #### Types of Isomerism - **Structural Isomers:** Different arrangements of atoms and bonds. - **Chain Isomers:** Different arrangements of the carbon skeleton (e.g., butane vs. 2-methylpropane). - **Positional Isomers:** Same carbon skeleton, but different positions of the functional group or substituents (e.g., propan-1-ol vs. propan-2-ol). - **Functional Group Isomers:** Different functional groups (e.g., ethanol vs. methoxymethane). - **Stereoisomers:** Same structural formula but different spatial arrangement of atoms. - **Geometric Isomers (cis-trans isomers):** Result from restricted rotation around a $\text{C}=\text{C}$ double bond or in cyclic structures. Requires two different groups on each carbon of the double bond. - **cis:** Identical groups on the same side. - **trans:** Identical groups on opposite sides. - **Optical Isomers (Enantiomers):** Non-superimposable mirror images. Occur when a molecule has a chiral carbon (a carbon atom bonded to four different groups). - Rotate plane-polarized light in opposite directions. - Have identical physical and chemical properties in a non-chiral environment. ### Reaction Types - **Substitution:** An atom or group of atoms is replaced by another atom or group of atoms. - **Free Radical Substitution:** Alkanes reacting with halogens in UV light (e.g., $\text{CH}_4 + \text{Cl}_2 \xrightarrow{UV} \text{CH}_3\text{Cl} + \text{HCl}$). - **Initiation:** $\text{Cl}_2 \xrightarrow{UV} 2\text{Cl}\cdot$ - **Propagation:** $\text{CH}_4 + \text{Cl}\cdot \rightarrow \text{CH}_3\cdot + \text{HCl}$ $\text{CH}_3\cdot + \text{Cl}_2 \rightarrow \text{CH}_3\text{Cl} + \text{Cl}\cdot$ - **Termination:** $\text{Cl}\cdot + \text{Cl}\cdot \rightarrow \text{Cl}_2$ $\text{CH}_3\cdot + \text{CH}_3\cdot \rightarrow \text{C}_2\text{H}_6$ $\text{CH}_3\cdot + \text{Cl}\cdot \rightarrow \text{CH}_3\text{Cl}$ - **Nucleophilic Substitution:** Halogenoalkanes reacting with nucleophiles ($\text{OH}^-, \text{CN}^-, \text{NH}_3$). - $\text{R-X} + \text{Nu}^- \rightarrow \text{R-Nu} + \text{X}^-$ - $\text{SN}_1$ (tertiary) vs. $\text{SN}_2$ (primary) mechanisms. - **Addition:** Atoms are added to an unsaturated molecule (alkene or alkyne), breaking the double/triple bond. - **Electrophilic Addition:** Alkenes reacting with $\text{H}_2, \text{X}_2, \text{HX}, \text{H}_2\text{O}$. - **Hydrogenation:** $\text{C}=\text{C} + \text{H}_2 \xrightarrow{Ni} \text{C-C}$ (alkane) - **Halogenation:** $\text{C}=\text{C} + \text{X}_2 \rightarrow \text{C(X)-C(X)}$ (dihaloalkane) - **Hydrohalogenation:** $\text{C}=\text{C} + \text{HX} \rightarrow \text{C(H)-C(X)}$ (halogenoalkane, Markovnikov's rule) - **Hydration:** $\text{C}=\text{C} + \text{H}_2\text{O} \xrightarrow{H_3PO_4} \text{C(H)-C(OH)}$ (alcohol) - **Elimination:** Small molecule (e.g., $\text{H}_2\text{O}$, $\text{HX}$) is removed from a molecule, forming an unsaturated product. - **Dehydration of Alcohols:** Alcohol $\xrightarrow{Conc. H_2SO_4} \text{Alkene} + \text{H}_2\text{O}$ - **Dehydrohalogenation of Halogenoalkanes:** Halogenoalkane $\xrightarrow{KOH (alc.)} \text{Alkene} + \text{HX}$ - **Oxidation:** Increase in oxygen content or decrease in hydrogen content. - **Combustion:** Organic compounds burn in oxygen to produce $\text{CO}_2$ and $\text{H}_2\text{O}$. - **Oxidation of Alcohols:** - **Primary alcohols:** $\text{RCH}_2\text{OH} \xrightarrow{K_2Cr_2O_7/H^+} \text{RCHO}$ (aldehyde) $\xrightarrow{K_2Cr_2O_7/H^+} \text{RCOOH}$ (carboxylic acid) - Aldehyde can be distilled off to prevent further oxidation. - **Secondary alcohols:** $\text{R}_2\text{CHOH} \xrightarrow{K_2Cr_2O_7/H^+} \text{R}_2\text{CO}$ (ketone) - **Tertiary alcohols:** Not easily oxidized. - **Reduction:** Decrease in oxygen content or increase in hydrogen content. - **Reduction of Carbonyls:** Aldehydes/ketones $\xrightarrow{NaBH_4 \text{ or } LiAlH_4} \text{Alcohols}$ ### Alcohols - **Functional Group:** Hydroxyl $(-\text{OH})$ - **Classification:** - **Primary (1°):** $-\text{OH}$ attached to a carbon bonded to one other carbon. - **Secondary (2°):** $-\text{OH}$ attached to a carbon bonded to two other carbons. - **Tertiary (3°):** $-\text{OH}$ attached to a carbon bonded to three other carbons. - **Properties:** - Higher boiling points than corresponding alkanes due to hydrogen bonding. - Short-chain alcohols are soluble in water (due to hydrogen bonding). - **Reactions:** - **Combustion:** Burns to $\text{CO}_2 + \text{H}_2\text{O}$. - **Oxidation:** See "Reaction Types" section. - **Esterification:** Alcohol + Carboxylic Acid $\rightleftharpoons$ Ester + Water (in presence of $\text{H}_2\text{SO}_4$ catalyst). - **Dehydration:** Alcohol $\xrightarrow{Conc. H_2SO_4} \text{Alkene} + \text{H}_2\text{O}$. ### Carboxylic Acids - **Functional Group:** Carboxyl $(-\text{COOH})$ - **Properties:** - Weak acids (partially dissociate in water): $\text{RCOOH} \rightleftharpoons \text{RCOO}^- + \text{H}^+$. - Higher boiling points than alcohols due to stronger hydrogen bonding (dimers). - Short-chain acids are soluble in water. - **Reactions:** - **Neutralization:** React with bases ($\text{NaOH}, \text{Na}_2\text{CO}_3, \text{NaHCO}_3$) to form salt and water (and $\text{CO}_2$ with carbonates). - **Esterification:** React with alcohols to form esters. ### Analytical Techniques (Brief) - **Mass Spectrometry (MS):** Determines molecular mass and structural information (fragmentation pattern). - **Infrared (IR) Spectroscopy:** Identifies functional groups based on characteristic bond vibrations (absorption of IR radiation). - **Key absorptions:** - $\text{O-H}$ (alcohols): Broad peak, $3200-3600 \text{ cm}^{-1}$ - $\text{O-H}$ (carboxylic acids): Very broad, $2500-3300 \text{ cm}^{-1}$ - $\text{C=O}$ (aldehydes, ketones, acids, esters): Strong peak, $1700-1750 \text{ cm}^{-1}$ - $\text{C-H}$: $2850-3000 \text{ cm}^{-1}$