Organic Chemistry Class 11

Cheatsheet Content

### Basic Principles of Organic Chemistry - **Definition:** Organic chemistry is the study of carbon compounds. - **Tetravalency of Carbon:** Carbon forms four bonds (single, double, or triple). - **Hybridization:** - sp³: Single bonds, tetrahedral, 109.5° bond angle (e.g., alkanes) - sp²: Double bond, trigonal planar, 120° bond angle (e.g., alkenes) - sp: Triple bond, linear, 180° bond angle (e.g., alkynes) - **Homologous Series:** A series of organic compounds with the same functional group and similar chemical properties, where successive members differ by a $-\text{CH}_2-$ group. - **Functional Group:** An atom or group of atoms responsible for the characteristic chemical properties of an organic compound. ### Nomenclature and Isomerism #### IUPAC Nomenclature - **Prefix:** Number of carbon atoms (Meth-, Eth-, Prop-, But-, etc.) - **Word Root:** Nature of carbon chain (e.g., -ane for single, -ene for double, -yne for triple) - **Suffix:** Functional group (e.g., -ol for alcohol, -al for aldehyde, -one for ketone, -oic acid for carboxylic acid) - **Rules:** 1. Longest continuous carbon chain. 2. Numbering starts from the end closer to the functional group/substituent. 3. Alphabetical order for multiple substituents. #### Isomerism - **Definition:** Compounds having the same molecular formula but different structural formulas or spatial arrangements. - **Structural Isomerism:** - **Chain Isomerism:** Different arrangement of carbon chain (e.g., n-butane, isobutane). - **Position Isomerism:** Different position of functional group or substituent (e.g., 1-propanol, 2-propanol). - **Functional Group Isomerism:** Different functional groups (e.g., ethanol, dimethylether). - **Metamerism:** Different alkyl groups attached to the functional group (e.g., methoxyethane, ethoxyethane). - **Tautomerism:** Dynamic equilibrium between two functional isomers (e.g., keto-enol tautomerism). - **Stereoisomerism:** Different spatial arrangement of atoms. - **Geometrical Isomerism (cis-trans):** Restricted rotation around double bond or ring (e.g., cis-2-butene, trans-2-butene). - **Optical Isomerism:** Chiral center, non-superimposable mirror images (enantiomers). ### Organic Reaction Mechanisms - **Bond Fission:** - **Homolytic Fission:** Each atom takes one electron, forming free radicals. - **Heterolytic Fission:** One atom takes both electrons, forming carbocations or carbanions. - **Electron Displacement Effects:** - **Inductive Effect (+I/-I):** Permanent displacement of sigma electrons along a chain due to electronegativity difference. - **Resonance Effect (+R/-R or Mesomeric Effect):** Delocalization of pi electrons or lone pair electrons within a conjugated system. - **Hyperconjugation (No Bond Resonance):** Delocalization of sigma electrons of C-H bond with an adjacent pi system or empty p-orbital. - **Electromeric Effect (+E/-E):** Temporary complete transfer of pi electrons towards one of the bonded atoms in the presence of an attacking reagent. - **Types of Organic Reactions:** - **Substitution Reactions:** One atom/group is replaced by another (e.g., halogenation of alkanes). - **Addition Reactions:** Atoms/groups add across a multiple bond (e.g., hydrogenation of alkenes). - **Elimination Reactions:** Atoms/groups are removed, forming a multiple bond (e.g., dehydration of alcohols). - **Rearrangement Reactions:** Atoms/groups migrate within the molecule. ### Hydrocarbons #### Alkanes (Saturated Hydrocarbons) - **General Formula:** $\text{C}_n\text{H}_{2n+2}$ - **Properties:** Nonpolar, unreactive, undergo free radical substitution. - **Reactions:** - **Halogenation:** $\text{CH}_4 + \text{Cl}_2 \xrightarrow{hv} \text{CH}_3\text{Cl} + \text{HCl}$ - **Combustion:** $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$ #### Alkenes (Unsaturated Hydrocarbons with C=C) - **General Formula:** $\text{C}_n\text{H}_{2n}$ - **Properties:** More reactive than alkanes due to pi bond, undergo electrophilic addition. - **Reactions:** - **Hydrogenation:** $\text{RCH=CHR'} + \text{H}_2 \xrightarrow{Ni, Pd, Pt} \text{RCH}_2\text{CH}_2\text{R'}$ - **Halogenation:** $\text{RCH=CHR'} + \text{Br}_2 \rightarrow \text{RCHBr-CHBrR'}$ (decolorizes bromine water) - **Hydrohalogenation:** $\text{RCH=CH}_2 + \text{HCl} \rightarrow \text{RCHCl-CH}_3$ (Markovnikov's Rule) - **Hydration:** $\text{RCH=CH}_2 + \text{H}_2\text{O} \xrightarrow{H^+} \text{RCH(OH)-CH}_3$ (Markovnikov's Rule) - **Ozonolysis:** Cleavage of C=C bond to form aldehydes/ketones. #### Alkynes (Unsaturated Hydrocarbons with C≡C) - **General Formula:** $\text{C}_n\text{H}_{2n-2}$ - **Properties:** Acidic terminal alkynes, undergo electrophilic addition. - **Reactions:** - **Hydrogenation:** $\text{RC≡CR'} + 2\text{H}_2 \xrightarrow{Ni, Pd, Pt} \text{RCH}_2\text{CH}_2\text{R'}$ - **Partial Hydrogenation:** $\text{RC≡CR'} + \text{H}_2 \xrightarrow{Lindlar's Cat.} \text{cis-RCH=CHR'}$ - **Halogenation:** $\text{RC≡CR'} + 2\text{Br}_2 \rightarrow \text{RCBr}_2\text{-CBr}_2\text{R'}$ - **Addition of HX:** Follows Markovnikov's rule, forms gem-dihalides. - **Acidity of Terminal Alkynes:** $\text{RC≡CH} + \text{NaNH}_2 \rightarrow \text{RC≡C}^-\text{Na}^+ + \text{NH}_3$ #### Aromatic Hydrocarbons (Benzene) - **Structure of Benzene:** Cyclic, planar, conjugated, 6 pi electrons (Hückel's Rule: 4n+2). - **Electrophilic Substitution Reactions:** - **Nitration:** $\text{C}_6\text{H}_6 + \text{HNO}_3 \xrightarrow{H_2SO_4} \text{C}_6\text{H}_5\text{NO}_2 + \text{H}_2\text{O}$ - **Halogenation:** $\text{C}_6\text{H}_6 + \text{Cl}_2 \xrightarrow{FeCl_3} \text{C}_6\text{H}_5\text{Cl} + \text{HCl}$ - **Sulfonation:** $\text{C}_6\text{H}_6 + \text{H}_2\text{SO}_4 \xrightarrow{\Delta} \text{C}_6\text{H}_5\text{SO}_3\text{H} + \text{H}_2\text{O}$ - **Friedel-Crafts Alkylation:** $\text{C}_6\text{H}_6 + \text{RCl} \xrightarrow{AlCl_3} \text{C}_6\text{H}_5\text{R} + \text{HCl}$ - **Friedel-Crafts Acylation:** $\text{C}_6\text{H}_6 + \text{RCOCl} \xrightarrow{AlCl_3} \text{C}_6\text{H}_5\text{COR} + \text{HCl}$ - **Directing Groups:** - **Ortho/Para directing (activating):** $-\text{OH}, -\text{NH}_2, -\text{CH}_3, -\text{Cl}$ (halogens are deactivating but o/p directing). - **Meta directing (deactivating):** $-\text{NO}_2, -\text{COOH}, -\text{CHO}, -\text{CN}$.