Comprehensive Organic Chemistry Study Guide: Alkanes, Alkenes, Nomenclature, and Reaction Mechanisms

Classification of Organic Compounds

• Hydrocarbons (الهيدروكربونات): Organic compounds containing only carbon ($C$) and hydrogen ($H$) atoms.

  • Aliphatic Hydrocarbons (الهيدروكربونات الأليفاتية):

    • Open-Chain Hydrocarbons (مفتوحة السلسلة):

      • Saturated (مشبعة): Alkanes (الألكانات), possessing single sigma ($\text{σ}$) covalent bonds. General molecular formula: $C_n H_{2n+2}$.

      • Unsaturated (غير مشبعة):

        • Alkenes (الألكينات): Hydrocarbons containing double bond(s) ($C=C$). General molecular formula: $C_n H_{2n}$.

        • Alkynes (الألكاينات): Hydrocarbons containing triple bond(s) ($C≡C$). General molecular formula: $C_n H_{2n-2}$.

    • Cyclic Saturated Hydrocarbons (حلقية مشبعة): Cycloalkanes (الألكانات الحلقية / سيكلو ألكانات), ring structures formed by single bonds. General molecular formula: $C_n H_{2n}$.

      • Cyclopropane (سيكلوبروبان): $C_3H_6$

      • Cyclobutane (سيكلوبيوتان): $C_4H_8$

      • Cyclopentane (سيكلوبنتان): $C_5H_{10}$

      • Cyclohexane (سيكلوهكسان): $C_6H_{12}$

  • Aromatic Hydrocarbons (الهيدروكربونات الأروماتية العطرية): Unsaturated cyclic ring structures with alternating single and double bonds.

    • Benzene (بنزين عطري): $C_6H_6$

    • Naphthalene (نفتالين): $C_{10}H_8$

    • Anthracene (أنثراسين): $C_{14}H_{10}$

• Hydrocarbon Derivatives (مشتقات الهيدروكربونات): Organic compounds containing carbon, hydrogen, and other elements such as oxygen ($O$) or nitrogen ($N$).

  • Alcohols (كحولات): Characterized by hydroxyl groups, e.g., Ethanol ($C_2H_5OH$).

IUPAC Nomenclature System for Alkanes

• Carbon Atom Root Prefixes ($C_1$ to $C_{10}$):

  • $C_1$: Meth- (ميث) $\rightarrow$ Methane ($CH_4$)

  • $C_2$: Eth- (إيث) $\rightarrow$ Ethane ($C_2H_6$)

  • $C_3$: Prop- (بروب) $\rightarrow$ Propane ($C_3H_8$)

  • $C_4$: But- (بيوت) $\rightarrow$ Butane ($C_4H_{10}$)

  • $C_5$: Pent- (بنت) $\rightarrow$ Pentane ($C_5H_{12}$)

  • $C_6$: Hex- (هكس) $\rightarrow$ Hexane ($C_6H_{14}$)

  • $C_7$: Hept- (هبت) $\rightarrow$ Heptane ($C_7H_{16}$)

  • $C_8$: Oct- (أوكت) $\rightarrow$ Octane ($C_8H_{18}$)

  • $C_9$: Non- (نون) $\rightarrow$ Nonane ($C_9H_{20}$)

  • $C_{10}$: Dec- (ديك) $\rightarrow$ Decane ($C_{10}H_{22}$)

• Substituents and Functional Groups:

  • Halogens (هالوجينات):

    • Fluoro group: $F-$ (فلورو)

    • Chloro group: $Cl-$ (كلورو)

    • Bromo group: $Br-$ (برومو)

    • Iodo group: $I-$ (يودو)

  • Nitro group: $-NO_2$ (نيترو)

  • Alkyl Groups (مجموعات الألكيل): Radical groups derived by removing one hydrogen atom from a saturated alkane ($R-$). General formula: $C_n H_{2n+1}$.

    • Methyl group: $-CH_3$ (مثيل)

    • Ethyl group: $-C_2H_5$ (إثيل)

    • Propyl group: $-C_3H_7$ (بروبيل)

    • Butyl group: $-C_4H_9$ (بيوتيل)

  • Aryl Group: Phenyl group: $-C_6H_5$ (فينيل)

• IUPAC Rules for Naming Branched Alkanes:

  1. Select the Longest Carbon Chain: Identify the longest continuous chain of carbon atoms to establish the parent alkane name.

  2. Number the Chain: Number the carbon chain starting from the end closest to any branch or substituent to give substituents the lowest possible set of locants.

  3. Alphabetical Ordering: List substituent names in alphabetical order before the parent alkane name (e.g., Bromo before Chloro, Chloro before Ethyl, Ethyl before Methyl).

• Nomenclature Examples:

  • $\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3$ $\rightarrow$ 2-Methylbutane (2-مثيل بيوتان)

  • $\text{CH}_3-\text{CH}_2-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3$ $\rightarrow$ 3-Methylpentane (3-مثيل بنتان)

  • $\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}(\text{CH}_3)-\text{CH}_3$ $\rightarrow$ 2,3-Dimethylbutane (2,3-ثنائي مثيل بيوتان)

  • $\text{CH}_3-\text{CH}_2-\text{CH}(\text{C}_2\text{H}_5)-\text{CH}_2-\text{CH}_2-\text{CH}_3$ $\rightarrow$ 3-Ethylhexane (3-إثيل هكسان)

  • $\text{CH}_3-\text{CH}(\text{Cl})-\text{CH}(\text{Br})-\text{CH}_3$ $\rightarrow$ 3-Bromo-2-chlorobutane (3-برومو-2-كلوروبيوتان)

  • $\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_2-\text{CH}(\text{CH}_3)-\text{CH}_3$ $\rightarrow$ 2,5-Dimethylheptane (2,5-ثنائي مثيل هبتان)

  • $\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}(\text{C}_2\text{H}_5)-\text{CH}_2-\text{CH}_2-\text{CH}_3$ $\rightarrow$ 3-Ethyl-2-methylhexane (3-إثيل-2-مثيل هكسان)

Alkanes / Paraffins

• Definition: Alkanes are aliphatic open-chain saturated hydrocarbons containing single covalent sigma ($\text{σ}$) bonds between carbon atoms.

• Common Name: Paraffins (البارافينات).

• General Formula: $C_n H_{2n+2}$

• Chemical Reactivity: Alkanes are relatively inert chemically (خاملة نسبياً غير نشطة كيميائياً) because all carbon-carbon and carbon-hydrogen bonds are strong single sigma ($\text{σ}$) bonds that require significant energy to break.

• Homologous Series (سلسلة متجانسة): A group of organic compounds sharing a general molecular formula, exhibiting similar chemical properties, and showing a gradual change in physical properties as molecular weight increases.

  • Methane ($CH_4$): Molar Mass = $12 + (4 \times 1) = 16\,g\,mol^{-1}$

  • Ethane ($C_2H_6$): Molar Mass = $(2 \times 12) + (6 \times 1) = 30\,g\,mol^{-1}$

  • Propane ($C_3H_8$): Molar Mass = $(3 \times 12) + (8 \times 1) = 44\,g\,mol^{-1}$

  • Butane ($C_4H_{10}$): Molar Mass = $(4 \times 12) + (10 \times 1) = 58\,g\,mol^{-1}$

  • Pentane ($C_5H_{12}$): Molar Mass = $(5 \times 12) + (12 \times 1) = 72\,g\,mol^{-1}$

• Physical Properties of Alkanes:

  • Gases ($C_1$ to $C_4$): Methane ($CH_4$), Ethane ($C_2H_6$), Propane ($C_3H_8$), Butane ($C_4H_{10}$).

  • Liquids ($C_5$ to $C_{17}$): Gasoline (جازولين) and Kerosene (كيروسين).

  • Solids ($C_{17}$ and higher): Paraffin wax (شمع البارافينات).

• Laboratory Preparation of Methane ($CH_4$):

  • Methane is prepared by the dry distillation of anhydrous sodium acetate with soda lime (a mixture of sodium hydroxide $NaOH$ and calcium oxide $CaO$):         $CH_3COONa + NaOH \xrightarrow{CaO} CH_4 + Na_2CO_3$

  • General formula for alkane preparation via sodium carboxylates:         $R-COONa + NaOH \xrightarrow{CaO} R-H + Na_2CO_3$

  • Examples:

    • Sodium propionate: $C_2H_5COONa + NaOH \xrightarrow{CaO} C_2H_6 + Na_2CO_3$

    • Sodium butyrate: $C_3H_7COONa + NaOH \xrightarrow{CaO} C_3H_8 + Na_2CO_3$

  • Synthesis of sodium acetate from acetic acid:         $CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O$

• Chemical Properties of Alkanes:

  • 1. Combustion (الاحتراق): Highly exothermic reaction yielding carbon dioxide, water vapor, and energy.         $CH_4 + 2O_2 \xrightarrow{\Delta} CO_2 + 2H_2O$

  • 2. Halogenation (الهاجنة / تفاعلات الإستبدال): Substitution reactions with halogens ($F_2, Cl_2, Br_2, I_2$) taking place in ultraviolet ($UV$) sunlight:

    • Step 1: $CH_4 + Cl_2 \xrightarrow{UV} CH_3Cl + HCl$ (Chloromethane / Methyl chloride - كلوروميثان / كلوريد المثيل)

    • Step 2: $CH_3Cl + Cl_2 \xrightarrow{UV} CH_2Cl_2 + HCl$ (Dichloromethane / Methylene chloride - ثنائي كلوروميثان)

    • Step 3: $CH_2Cl_2 + Cl_2 \xrightarrow{UV} CHCl_3 + HCl$ (Trichloromethane / Chloroform - ثلاثي كلوروميثان / كلوروفورم)

    • Step 4: $CHCl_3 + Cl_2 \xrightarrow{UV} CCl_4 + HCl$ (Tetrachloromethane / Carbon tetrachloride - رابع كلوريد الكربون / رباعي كلوروميثان)

• Halogenated Alkane Derivatives and Applications:

  • Chloroform ($CHCl_3$): Formerly used as an anesthetic in medicine; discontinued due to difficulty in controlling precise dosage leading to toxicity.

  • Halothane ($CF_3-CHClBr$ / 2-Bromo-2-chloro-1,1,1-trifluoroethane): Used as a safe modern anesthetic.

  • 1,1,1-Trichloroethane ($CH_3-CCl_3$): Used in dry cleaning solutions.

  • Freons (الفريونات): Chlorofluorocarbons (e.g., $CF_4$, $CF_2Cl_2$). Easily liquefied, non-toxic, non-corrosive, cheap; used as refrigerants in cooling devices and propellants for aerosols.

  • Carbon Tetrachloride ($CCl_4$): Important non-polar organic solvent.

• Economic Importance of Methane:

  • Obtaining Divided Carbon / Black Carbon (أسود الكربون / الكربون المجزأ): Thermal decomposition of methane at high temperature in the absence of air:         $CH_4 \xrightarrow{1000^\circ\text{C}} C + 2H_2$         Applications: Manufacturing car tires, black printing ink, paints, and shoe varnish.

  • Obtaining Water Gas (الغاز المائي): Catalytic reaction with water vapor:         $CH_4 + H_2O \xrightarrow{725^\circ\text{C}} CO + 3H_2$         Applications: Used as a liquid fuel and as a reducing agent in industrial contexts.

Alkenes / Olefins

• Definition: Alkenes are aliphatic open-chain unsaturated hydrocarbons containing at least one carbon-carbon double bond ($C=C$).

• Common Name: Olefins (الأوليفينات).

• General Formula: $C_n H_{2n}$

• Chemical Reactivity: Alkenes are significantly more reactive than alkanes due to the presence of a double bond composed of one strong sigma ($\text{σ}$) bond and one weak pi ($\text{π}$) bond that is easily broken during addition reactions.

• Homologous Series and Molar Masses:

  • Ethene ($C_2H_4$): Molar Mass = $(2 \times 12) + (4 \times 1) = 28\,g\,mol^{-1}$

  • Propene ($C_3H_6$): Molar Mass = $(3 \times 12) + (6 \times 1) = 42\,g\,mol^{-1}$

  • Butene ($C_4H_8$): Molar Mass = $(4 \times 12) + (8 \times 1) = 56\,g\,mol^{-1}$

• Physical States:

  • Gases ($C_2$ to $C_4$): Ethene ($C_2H_4$), Propene ($C_3H_6$), Butene ($C_4H_8$).

  • Liquids ($C_5$ to $C_{15}$): Liquid hydrocarbons.

  • Solids ($C_{15}$ and higher): Higher molecular weight alkanes/alkenes.

• Laboratory Preparation of Ethene ($C_2H_4$):

  • Ethene is prepared via catalytic dehydration of ethanol using concentrated sulfuric acid ($H_2SO_4$) at $180^\circ\text{C}$:         $C_2H_5OH \xrightarrow[180^\circ\text{C}]{H_2SO_4} C_2H_4 + H_2O$

  • General reaction for alkene preparation from alcohols:         $C_n H_{2n+1}OH \xrightarrow[180^\circ\text{C}]{H_2SO_4} C_n H_{2n} + H_2O$

  • Example with Propanol:         $C_3H_7OH \xrightarrow[180^\circ\text{C}]{H_2SO_4} C_3H_6 + H_2O$

• Chemical Reactions of Alkenes:

  • 1. Combustion (الاحتراق):         $C_2H_4 + 3O_2 \xrightarrow{\Delta} 2CO_2 + 2H_2O$

  • 2. Hydrogenation (الهدرجة - تفاعل إضافة): Addition of hydrogen gas ($H_2$) in the presence of a heated nickel ($Ni$) or platinum ($Pt$) catalyst to yield saturated alkanes:         $H_2C=CH_2 + H_2 \xrightarrow[Pt / Ni]{\Delta} CH_3-CH_3$

  • 3. Halogenation (الهلجنة - تفاعل إضافة): Addition of halogens ($F_2, Cl_2, Br_2, I_2$).

    • Test for Unsaturation: Addition of red bromine dissolved in carbon tetrachloride ($Br_2 / CCl_4$). The red color vanishes upon reaction with unsaturated bonds.         $H_2C=CH_2 + Br_2 \xrightarrow{CCl_4} CH_2Br-CH_2Br$         Product: 1,2-Dibromoethane (1,2-ثنائي برومو إيثان).

Unsymmetrical Addition Reactions and Markovnikov's Rule

• Catalytic Hydration (الهيدرة الحفزية): Addition of water ($H_2O$) to alkenes in the presence of dilute sulfuric acid ($H_2SO_4$) catalyst at $110^\circ\text{C}$ to yield alcohols:     $C_2H_4 + H_2O \xrightarrow[110^\circ\text{C}]{H_2SO_4} C_2H_5OH$

• Symmetrical vs. Unsymmetrical Alkenes:

  • Symmetrical Alkene (ألكين متماثل): An alkene in which the two double-bonded carbon atoms carry equal numbers of hydrogen atoms.

    • Example: Ethene ($H_2C=CH_2$).

  • Unsymmetrical Alkene (ألكين غير متماثل): An alkene in which the two double-bonded carbon atoms carry different numbers of hydrogen atoms.

    • Example: Propene ($CH_3-CH=CH_2$).

• Symmetrical vs. Unsymmetrical Reagents:

  • Symmetrical Reagent: $H_2$, $Br_2$, $Cl_2$

  • Unsymmetrical Reagent: Hydrogen halides ($HX$ like $HBr$, $HCl$, $HI$) or water ($H-OH$).

• Markovnikov's Rule (قاعدة ماركونيكوف):     When an unsymmetrical reagent (such as $HX$ or $H_2O$) is added to an unsymmetrical alkene, the positive hydrogen part ($H^+$) attaches to the double-bonded carbon atom bearing the greater number of hydrogen atoms, while the negative part ($X^-$ or $OH^-$) attaches to the double-bonded carbon atom bearing fewer hydrogen atoms.

• Application Example (Addition of Hydrogen Bromide to Propene):

  • Reaction:         $CH_3-CH=CH_2 + HBr \rightarrow CH_3-CHBr-CH_3$

  • Result: 2-Bromopropane (2-برومو بروبان) is selectively formed as the primary product, rather than 1-bromopropane.