Study Notes – NEET Chemistry
Topic: General Organic Chemistry & Hydrocarbons (GOC & Hydrocarbons)
These notes are designed for quick, clear revision.
They cover the basic concepts that appear in the NEET exam, key facts, a worked example, and a revision summary.
1. Simple Explanation
Organic chemistry is the chemistry of carbon‑containing molecules.
Hydrocarbons – the simplest organic compounds – contain only carbon (C) and hydrogen (H).
They form the backbone of more complex organic molecules and are classified by the type of C–C bonds they contain:
| Class | Bond type | General formula | Example |
|---|---|---|---|
| Alkanes | Single C–C bonds (saturated) | CₙH₂ₙ₊₂ | Methane (CH₄) |
| Alkenes | One double C=C (unsaturated) | CₙH₂ₙ | Ethene (C₂H₄) |
| Alkynes | One triple C≡C (unsaturated) | CₙH₂ₙ₋₂ | Ethyne (C₂H₂) |
| Aromatic hydrocarbons | Delocalised π system (benzene ring) | C₆H₆ | Benzene |
Key points:
- Saturation – alkanes are saturated (no π bonds).
- Unsaturation – alkenes & alkynes are unsaturated (contain π bonds).
- Reactivity – π bonds are more reactive than σ bonds → addition reactions are common for alkenes/alkynes.
- Isomerism – hydrocarbons can be structural (different connectivity) or stereochemical (different spatial arrangement).
2. Key Points
| Topic | Main Ideas |
|---|---|
| Molecular Formula & Degree of Unsaturation | DU = (2C + 2 – H)/2 (ignoring halogens & N). DU = 0 → saturated; >0 → π bonds or rings. |
| IUPAC Naming | 1. Identify longest carbon chain (root). 2. Number chain to give lowest locants to functional groups/alkene/alkyne. 3. Prefixes for substituents (methyl, ethyl, etc.). 4. Combine with suffixes (-ane, -ene, -yne, -benzene). |
| Alkane Substitution | Only SN1 & SN2 (rarely). 1,2‑addition of halides via radical halogenation. |
| Alkene/Alkyne Addition Reactions | 1. Hydration → alcohol (acid‑catalysed). 2. Halogenation → di‑halo compounds. 3. Hydrohalogenation → alkyl halides. 4. Hydrogenation → alkanes. |
| Alkane Isomerism | Structural isomers: chain branching, position of substituent. 1‑Butanol vs 2‑butanol. |
| Alkene Isomerism | Cis–trans (E/Z) for alkenes with two different substituents on each carbon. |
| Aromaticity | 4n+2 π electrons rule (Hückel). Delocalised ring → stable, undergoes electrophilic substitution (e.g., nitration, halogenation). |
| Common Reactions | 1. Hydrogenation (Cu catalyst). 2. Halogenation (free radical). 3. Hydrohalogenation (HBr, HI). 4. Hydration (H₂O, H₂SO₄). 5. Oxidation of alkanes (no simple reaction). 6. Oxidation of alkenes (epoxidation, dihydroxylation). |
| Functional Groups in Hydrocarbons | Alkyl (R–), alkenyl (R=C–), alkynyl (R≡C–), aryl (C₆H₅–). |
| Stereochemistry | Chirality (asymmetric carbon). Conformational (rotatable bonds). |
| Neat Reaction Conditions | Temperature, catalysts (Pt, Pd, Ni for hydrogenation; FeCl₃ for halogenation, etc.). |
Tip: Memorise the degree of unsaturation formula – it’s a quick way to identify the type of hydrocarbon.
3. Worked Example
Problem:
Predict the product and mechanism when ethene (C₂H₄) is treated with aqueous H₂SO₄ followed by NaOH.
Step‑by‑step:
- Hydration of Ethene
- Catalyst: H₂SO₄ (protonates double bond).
- Carbocation formation: CH₃–CH₂⁺ (more stable secondary).
- Water attack: H₂O adds to carbocation → CH₃–CH₂–OH (ethanol).
- Proton transfer & deprotonation: Loss of H⁺ gives neutral ethanol.
- Overall:
[ \text{CH}_2=\text{CH}_2 + \