Introduction, Classification, Nomenclature, and Structures

  • Introduction:
    • Alcohols, phenols, and ethers are basic compounds for detergents, antiseptics, and fragrances, respectively.
    • Substitution of hydrogen in hydrocarbons by other atoms/groups creates new compounds with different properties.
    • Alcohols and phenols are formed by replacing a hydrogen atom in aliphatic and aromatic hydrocarbons, respectively, with an -OH group.
    • These compounds have wide industrial and daily life applications (e.g., ethanol in spirit for polishing, -OH groups in sugar, cotton, paper).
  • Definitions:
    • Alcohol: Contains one or more hydroxyl (-OH) groups directly attached to carbon atom(s) of an aliphatic system \(\mathrm{(e.g.,\ CH_3OH)}\).
    • Phenol: Contains -OH group(s) directly attached to carbon atom(s) of an aromatic system \(\mathrm{(e.g.,\ C_6H_5OH)}\).
    • Ether: Formed by substituting a hydrogen atom in a hydrocarbon by an alkoxy (-OR) or aryloxy (-OAr) group \(\mathrm{(e.g.,\ CH_3OCH_3)}\). Ethers can also be visualized as compounds formed by substituting the hydrogen of an alcohol’s or phenol’s hydroxyl group with an alkyl or aryl group.
  • Classification:

     

    • Alcohols and Phenols: Classified as mono-, di-, tri-, or polyhydric based on the number of hydroxyl groups (one, two, three, or many).

       

      • Monohydric alcohol: \(\mathrm{C_2H_5OH}\)
      • Dihydric alcohol: \(\mathrm{CH_2OHCHOHCH_2OH}\)
      • Trihydric alcohol: \(\mathrm{CH_2OH{-}CHOH{-}CH_2OH}\)
    • Monohydric Alcohols Classification (based on hybridisation of carbon with -OH):

       

      • (i) Compounds containing Csp3​-OH bond: -OH attached to an sp3 hybridised carbon of an alkyl group.

         

        • Primary (1°): -OH attached to a primary carbon \(\mathrm{(e.g.,\ {-}CH_2{-}OH)}\).
        • Secondary (2°): -OH attached to a secondary carbon \(\mathrm{(e.g.,\ >CH{-}OH)}\).
        • Tertiary (3°): -OH attached to a tertiary carbon \(\mathrm{(e.g.,\ >C{-}OH)}\).
        • Allylic Alcohols: -OH attached to an sp3 hybridised carbon adjacent to a C=C double bond (allylic carbon). Can be primary, secondary, or tertiary.

           

          • Primary allylic: \(\mathrm{CH_2{=}CH{-}CH_2{-}OH}\)
        • Benzylic Alcohols: -OH attached to an sp3-hybridised carbon atom next to an aromatic ring. Can be primary, secondary, or tertiary.
      • (ii) Compounds containing Csp2​-OH bond: -OH group bonded to a C=C double bond (vinylic carbon) or to an aryl carbon. Also known as vinylic alcohols \(\mathrm{(e.g.,\ CH_2{=}CH{-}OH)}\).
    • Phenols Classification:
      • Monohydric: One -OH group.
      • Dihydric: Two -OH groups.
      • Trihydric: Three -OH groups.
    • Ethers: Classified based on the alkyl/aryl groups attached to the oxygen atom.

       

      • Simple or Symmetrical: Both groups are the same \(\mathrm{(e.g.,\ Diethyl\ ether,\ C_2H_5OC_2H_5)}\).
      • Mixed or Unsymmetrical: The two groups are different \(\mathrm{(e.g.,\ C_2H_5OCH_3,\ C_2H_5OC_6H_5)}\).
  • Nomenclature:
    • (a) Alcohols:
      • Common Name: Derived from the common name of the alkyl group + “alcohol” \(\mathrm{(e.g.,\ CH_3OH\ is\ methyl\ alcohol)}\).
      • IUPAC System: Derived from the alkane name by replacing ‘e’ with ‘ol’.

         

        • Longest carbon chain with -OH is parent chain, numbered from end nearest to -OH.
        • Positions of -OH and other substituents indicated by numerals.
        • Polyhydric Alcohols: Retain ‘e’ of alkane, add ‘ol’ with multiplicative prefix (di, tri, etc.) and appropriate locants \(\mathrm{(e.g.,\ ethane\text{-}1,2\text{-}diol\ for\ HO{-}CH_2{-}CH_2{-}OH)}\).
        • Cyclic Alcohols: Use prefix ‘cyclo’, -OH group attached to C-1.
    • (b) Phenols:
      • Phenol: Common name, also accepted IUPAC name for simplest hydroxy derivative of benzene.
      • Substituted Phenols: Ortho (1,2-), meta (1,3-), para (1,4-) used in common names.
      • Dihydroxy Derivatives: Named as benzenediols (e.g., Benzene-1,2-diol for Catechol).
    • (c) Ethers:
      • Common Names: Alkyl/aryl groups written alphabetically + “ether” \(\mathrm{(e.g.,\ CH_3OC_2H_5\ is\ ethylmethyl\ ether)}\). If same alkyl groups, use ‘di’ prefix \(\mathrm{(e.g.,\ C_2H_5OC_2H_5\ is\ diethyl\ ether)}\).
      • IUPAC System: Regarded as hydrocarbon derivatives where H atom replaced by -OR or -OAr group. Larger (R) group is parent hydrocarbon.
  • Structures of Functional Groups:

     

    • Alcohols: Oxygen of -OH attached to carbon by a sigma (σ) bond formed by overlap of sp3 hybridised C orbital with sp3 hybridised O orbital.

       

      • Bond angle in alcohols (e.g., methanol’s C-O-H angle is 108.9∘) is slightly less than tetrahedral angle (109∘28′) due to repulsion between unshared electron pairs of oxygen.
      • C-O bond length in methanol is 142 pm, O-H bond length is 96 pm.
    • Phenols: -OH group attached to sp2 hybridised carbon of aromatic ring.

       

      • C-O bond length (136 pm) is slightly less than in methanol. Reasons: (i) Partial double bond character due to conjugation of oxygen’s unshared electron pair with aromatic ring, (ii) sp2 hybridised state of carbon to which oxygen is attached.
      • C-O-H angle in phenol is 109∘.
    • Ethers: Four electron pairs (two bond pairs, two lone pairs) on oxygen are approximately in a tetrahedral arrangement.

       

      • Bond angle (e.g., 111.7∘ in methoxymethane) is slightly greater than tetrahedral angle due to repulsive interaction between two bulky (-R) groups.
      • C-O bond length (141 pm) is almost same as in alcohols.
      • C-H bond length is 109 pm.
Part 1: Introduction to Work, Energy, and Scalar Product Chapter Notes: • The Scalar Product (Dot Product): o Definition: $$A⋅B=A B cos θ$$ o Geometric Interpretation: $$A⋅B=A(B cos θ) $$ $$=B(A cos θ) $$ o Properties of Scalar Product:  Commutative Law: $$A⋅B=B⋅A$$  Distributive Law: A $$ (B+C)=A⋅B+A⋅C$$  Multiplication by a real number $$λ: A$$ $$ (λ B)=λ(A⋅B) $$ o Scalar Product of Unit Vectors: $$i^⋅j^=j^⋅j^=k^⋅k^=1$$ $$j^=j^⋅k^=k^⋅i^=0$$ o Scalar Product in Component Form: $$A=Axi^+Ayj^+Azk^ B=Bxi^+Byj^+Bzk^A⋅B=(Axi^+Ayj^+Azk^)⋅(Bxi^+Byj^+Bzk^) $$ $$=AxBx+AyBy+AzBz$$ o Self-Dot Product: $$A.A=AxAx+AyAy+AzAz$$ $$A2=Ax2+Ay2+Az2$$ since $$A⋅A=∣A∣∣A∣cos 0=A2. $$ o If A and B are perpendicular: $$A⋅B=0$$ Part 2: Work-Energy Theorem and Types of Work Chapter Notes: • Notions of Work and Kinetic Energy: The Work-Energy Theorem: o Rectilinear motion under constant acceleration: $$v2−ut2=2 $$as o Multiplying by m/2: $$21mv2−21mu2=mas=Fs $$ o Generalizing to three dimensions: $$v2−u2=2 a.d $$ $$21mv2−21mu2=ma $$.d=F.d o Work-Energy (WE) Theorem: $$Kf−Ki=W $$ • Work: o Definition: $$W=(F cos θ)d=F.d $$ • Work Done by a Variable Force: o For small displacement $$Δx: ΔW=F(x)Δx $$ o Total work done (summation): $$W≡∑xixfF(x)Δx $$ o Total work done (definite integral): $$W=limΔx→0∑xixfF(x)Δx$$ =∫xiyF(x)dx $$ • The Work-Energy Theorem for a Variable Force: o Time rate of change of kinetic energy: $$dtdK=dtd(21m v2)$$ =mdtdvv$$ =Fv$$ =Fdtdx $$ o Integrating from initial to final position: $$dK=Fdx $$ $$Kf−Ki=∫xixfFdx $$ o WE Theorem for variable force: $$Kf−Ki=W $$ o Modified WE Theorem (with non-conservative force): $$Δ(K+V)=FncΔx $$ $$ΔE=FncΔx $$ $$Ef−Ei=Wne $$

This MCQ module is based on: Introduction, Classification, Nomenclature, and Structures

This assessment will be based on: Introduction, Classification, Nomenclature, and Structures

  • Real-Life Connections & General Knowledge:
    • The ubiquitous presence of -OH containing compounds in daily life (sugar, cotton, paper, furniture polish) emphasizes the practical relevance of organic chemistry.
    • The systematic classification and nomenclature (IUPAC, common names, ortho/meta/para) are essential for clear communication in chemistry, a fundamental skill required in all chemistry competitive exams.
  • Case-based Scenarios & Reasoning:
    • Scenario 1: A student is given the molecular formula C4​H10​O and is asked to draw all possible isomeric alcohols.
      • Question: Classify each isomer as primary, secondary, or tertiary, and assign its IUPAC name.
      • Reasoning: This tests the ability to apply classification rules based on the carbon attached to -OH and IUPAC naming conventions for alcohols.
    • Scenario 2: Two organic compounds, A and B, both contain a hydroxyl group. Compound A shows characteristic reactions of alcohols but also exhibits reactivity at a double bond. Compound B reacts primarily as a phenol.
      • Question: Propose possible structural classifications for A and B based on the position of their hydroxyl groups.
      • Reasoning: This assesses understanding of allylic/vinylic alcohols vs. phenols based on bonding characteristics and reactivity implied.
  • Conceptual Application:
    • Hybridization and Bond Angles/Lengths: Analyze how the hybridization state of the carbon atom bonded to oxygen (sp3 in alcohols, sp2 in phenols) influences bond lengths and angles, particularly the slight differences from ideal tetrahedral angles due to lone pair repulsions or steric hindrance.
    • Resonance and Partial Double Bond Character: Explain how the conjugation of oxygen’s lone pair with the aromatic ring in phenols leads to partial double bond character in the C-O bond and its shorter length compared to alcohols.
    • Structural Basis of Classification: Discuss how the classification of alcohols and phenols based on the number of hydroxyl groups and the hybridization of the carbon atom to which they are attached provides a systematic approach to understanding their chemical properties.
  • Numerical/Data Interpretation (if applicable):
    • Methanol bond angles: C-O-H 108.9∘.
    • Methanol bond lengths: C-O 142 pm, O-H 96 pm.
    • Phenol C-O bond length: 136 pm.
    • Methoxymethane bond angle: C-O-C 111.7∘.
    • Methoxymethane C-O bond length: 141 pm.
  • Comparative & Analytical Points:
    • Compare and Contrast: Differentiate between alcohols, phenols, and ethers based on the attachment of the oxygen atom (aliphatic C, aromatic C, or between two R/Ar groups) and their general formula.
    • Distinguish Classification Types: Explain the difference between primary, secondary, and tertiary alcohols, and allylic/benzylic alcohols, providing structural examples for each.
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