Nomenclature, Methods of Preparation — Revision Notes

⚡ 30-Second Revision

Alcohols — R-OH, -OH group on saturated carbon.
Nomenclature — Alkane-e + -ol. Number -OH lowest.
From Alkenes

- Acid-catalyzed Hydration: H$_2$O, H$^+$. Markovnikov. Carbocation rearrangements possible. - Hydroboration-Oxidation (HBO): (i) BH$_3$.THF, (ii) H$_2$O$_2$, NaOH. Anti-Markovnikov. Syn addition.

From Carbonyls (Reduction)

- Aldehydes (RCHO) $\rightarrow$ Primary Alcohols (RCH$_2$OH). - Ketones (RCOR') $\rightarrow$ Secondary Alcohols (RCH(OH)R'). - Carboxylic Acids (RCOOH) $\rightarrow$ Primary Alcohols (RCH$_2$OH). - Esters (RCOOR') $\rightarrow$ Two Alcohols (RCH$_2$OH + R'OH). - Reagents: LiAlH$_4$ (strong, non-selective); NaBH$_4$ (milder, selective for aldehydes/ketones).

From Grignard Reagents (RMgX)

- Formaldehyde (HCHO) $\rightarrow$ Primary Alcohol. - Other Aldehydes (R'CHO) $\rightarrow$ Secondary Alcohol. - Ketones (R'COR'') $\rightarrow$ Tertiary Alcohol. - Esters (R'COOR'') $\rightarrow$ Tertiary Alcohol (with excess Grignard). - Conditions: Anhydrous, followed by H$_3$O$^+$.

From Alkyl Halides — RX + aq. KOH/NaOH $\rightarrow$ ROH (S$_N$2 for primary, S$_N$1 for tertiary).
Industrial — Fermentation (Ethanol), Hydration of Ethene (Ethanol), Water Gas (Methanol).

2-Minute Revision

Alcohols, characterized by the -OH group, are named by replacing the alkane's '-e' with '-ol', ensuring the -OH group gets the lowest possible number. Key preparation methods include converting alkenes via two distinct routes: acid-catalyzed hydration (Markovnikov addition, potential rearrangements) and hydroboration-oxidation (anti-Markovnikov, syn addition).

Carbonyl compounds like aldehydes and ketones are reduced to primary and secondary alcohols, respectively, using reagents such as NaBH$_4$ (selective for aldehydes/ketones) or LiAlH$_4$ (stronger, reduces carboxylic acids and esters too).

Grignard reagents are crucial for C-C bond formation: formaldehyde yields primary alcohols, other aldehydes yield secondary, and ketones yield tertiary alcohols. Alkyl halides can be hydrolyzed to alcohols using aqueous KOH/NaOH.

Remember the specific conditions and outcomes for each method, especially the regioselectivity and the type of alcohol produced. Industrial methods like fermentation for ethanol and synthesis gas for methanol are also important factual points.

5-Minute Revision

Alcohols are organic compounds with a hydroxyl (-OH) group attached to a saturated carbon. Their IUPAC nomenclature involves identifying the longest carbon chain containing the -OH, replacing the alkane suffix '-e' with '-ol', and numbering the chain to give the -OH group the lowest possible position. For example, CH$_3$CH(OH)CH$_3$ is propan-2-ol.

Methods of Preparation:

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From Alkenes:

* **Acid-catalyzed hydration (H$_2$O, H$^+$):** Follows Markovnikov's rule, forming the more substituted alcohol. Carbocation intermediates can lead to rearrangements. E.g., Propene $\rightarrow$ Propan-2-ol. * **Hydroboration-oxidation (i) BH$_3$.THF, (ii) H$_2$O$_2$, NaOH):** Anti-Markovnikov addition, yielding the less substituted alcohol. It's a syn addition. E.g., Propene $\rightarrow$ Propan-1-ol.

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From Carbonyl Compounds (Reduction):

* Aldehydes (RCHO) and Ketones (RCOR'): Reduced to primary and secondary alcohols, respectively. Reagents: NaBH$_4$ (milder, selective for aldehydes/ketones) or LiAlH$_4$ (stronger, reduces almost all carbonyls).

* *Example:* CH$_3$CHO (ethanal) $\xrightarrow{NaBH_4}$ CH$_3$CH$_2$OH (ethanol, primary). * *Example:* CH$_3$COCH$_3$ (propanone) $\xrightarrow{NaBH_4}$ CH$_3$CH(OH)CH$_3$ (propan-2-ol, secondary).

* Carboxylic Acids (RCOOH) and Esters (RCOOR'): Reduced to primary alcohols using LiAlH$_4$. NaBH$_4$ is generally ineffective. * *Example:* CH$_3$COOH (acetic acid) $\xrightarrow{LiAlH_4}$ CH$_3$CH$_2$OH (ethanol, primary).

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From Grignard Reagents (RMgX): — These are powerful nucleophiles forming new C-C bonds.

* Formaldehyde (HCHO): Yields primary alcohols. E.g., HCHO + CH$_3$MgBr $\rightarrow$ CH$_3$CH$_2$OH. * Other Aldehydes (R'CHO): Yields secondary alcohols. E.g., CH$_3$CHO + CH$_3$MgBr $\rightarrow$ CH$_3$CH(OH)CH$_3$. * Ketones (R'COR''): Yields tertiary alcohols. E.g., CH$_3$COCH$_3$ + CH$_3$MgBr $\rightarrow$ (CH$_3$)$_3$COH. * Important: Grignard reagents react with acidic protons (water, alcohols), so anhydrous conditions are crucial.

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From Alkyl Halides (RX): — Reaction with aqueous KOH or NaOH via S$_N$2 (for primary) or S$_N$1 (for tertiary) mechanisms yields alcohols. E.g., CH$_3$CH$_2$Cl + aq. KOH $\rightarrow$ CH$_3$CH$_2$OH.

Key takeaways for NEET: Understand the regioselectivity (Markovnikov vs. anti-Markovnikov), stereoselectivity (syn addition), and the type of alcohol produced (primary, secondary, tertiary) for each method. Pay close attention to reagent specificity (e.g., NaBH$_4$ vs. LiAlH$_4$) and potential carbocation rearrangements.

Prelims Revision Notes

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Nomenclature Basics — Alcohols are R-OH. IUPAC: Alkane-e + -ol. Number chain from end closest to -OH. If multiple -OH, use diol, triol, etc., and keep '-e' (e.g., ethane-1,2-diol). Common names: alkyl alcohol (e.g., methyl alcohol).
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Preparation from Alkenes

* Acid-catalyzed Hydration: H$_2$O, H$^+$. Markovnikov addition (OH on more substituted carbon). Carbocation intermediate, so rearrangements (hydride/alkyl shifts) are possible. Not stereospecific. * Hydroboration-Oxidation (HBO): (i) BH$_3$.THF, (ii) H$_2$O$_2$, NaOH. Anti-Markovnikov addition (OH on less substituted carbon). Syn addition (H and OH add to same face). No rearrangements.

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Preparation from Carbonyl Compounds (Reduction)

* Aldehydes (RCHO) $\rightarrow$ Primary Alcohols (RCH$_2$OH). * Ketones (RCOR') $\rightarrow$ Secondary Alcohols (RCH(OH)R'). * Carboxylic Acids (RCOOH) $\rightarrow$ Primary Alcohols (RCH$_2$OH).

* Esters (RCOOR') $\rightarrow$ Primary Alcohols (RCH$_2$OH + R'OH). * Reducing Agents: * **LiAlH$_4$**: Strong, reduces aldehydes, ketones, carboxylic acids, esters. Requires anhydrous conditions, followed by aqueous workup.

* **NaBH$_4$**: Milder, selectively reduces aldehydes and ketones. Does not reduce carboxylic acids, esters, or C=C double bonds. Can be used in protic solvents. * **Catalytic Hydrogenation (H$_2$/Ni, Pt, Pd)**: Reduces aldehydes and ketones to alcohols, and alkenes to alkanes.

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Preparation from Grignard Reagents (RMgX)

* RMgX + Formaldehyde (HCHO) $\rightarrow$ Primary Alcohol. * RMgX + Other Aldehydes (R'CHO) $\rightarrow$ Secondary Alcohol. * RMgX + Ketones (R'COR'') $\rightarrow$ Tertiary Alcohol. * RMgX + Esters (R'COOR'') $\rightarrow$ Tertiary Alcohol (with excess Grignard). * Crucial: Grignard reagents are strong bases and nucleophiles; react with any acidic proton (H$_2$O, ROH, RCOOH). Must be used under anhydrous conditions.

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Preparation from Alkyl Halides (RX)

* RX + aqueous KOH/NaOH $\rightarrow$ ROH (Nucleophilic substitution, S$_N$2 for primary, S$_N$1 for tertiary). Competing E2 with alcoholic KOH.

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Preparation from Primary Amines (RNH$_2$) — RNH$_2$ + HNO$_2$ (NaNO$_2$/HCl) $\rightarrow$ ROH + N$_2$. Not synthetically useful due to rearrangements and low yields for aliphatic amines.
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Industrial Methods

* Ethanol: Fermentation of sugars (C$_6$H$_{12}$O$_6$ $\xrightarrow{Yeast}$ 2C$_2$H$_5$OH + 2CO$_2$) or hydration of ethene (CH$_2$=CH$_2$ + H$_2$O $\xrightarrow{H_3PO_4}$ C$_2$H$_5$OH). * Methanol: From synthesis gas (CO + 2H$_2$ $\xrightarrow{ZnO/Cr_2O_3}$ CH$_3$OH).

Vyyuha Quick Recall

To remember Grignard products: For Primary, Always Secondary, Ketones Tertiary.

Formaldehyde $\rightarrow$ Primary Alcohol
Aldehydes (other) $\rightarrow$ Secondary Alcohol
Ketones $\rightarrow$ Tertiary Alcohol