The order of reactivity of alcohols with hydrogen halides (HX, like HCl, HBr, HI) depends mainly on how easily the C–OH bond can be broken and replaced by halogen.

Key points:

• The reaction proceeds either via carbocation formation (SN1) or direct displacement (SN2) depending on the substrate.
• Carbocation stability (tertiary > secondary > primary) governs the rate in SN1 cases.
• Resonance-stabilized carbocations (benzylic, allylic) are even more reactive than tertiary.

Reactivity order:

Benzylic alcohol > Allylic alcohol > Tertiary alcohol > Secondary alcohol > Primary alcohol

Explanation:

1. Benzylic alcohols → form benzylic carbocations stabilized by resonance with aromatic ring → very fast.
2. Allylic alcohols → form allylic carbocations stabilized by resonance with adjacent double bond → also very fast.
3. Tertiary alcohols → form stable 3° carbocations → faster than 2° or 1°.
4. Secondary alcohols → less stable carbocation, slower.
5. Primary alcohols → do not form stable carbocations easily, react only by SN2 mechanism with HX, so they are slowest.

Final order:
Benzyl > Allyl > 3° > 2° > 1°

Ethylidene dibromide
Structure: CH₃–CHBr₂
IUPAC name: 1,1-dibromoethane

Isopropylidene dichloride
Structure: (CH₃)₂CCl₂
IUPAC name: 2,2-dichloropropane

Ethylene dibromide
Structure: Br–CH₂–CH₂–Br
IUPAC name: 1,2-dibromoethane

Isobutene dibromide (addition product of Br₂ across 2-methylprop-1-ene)
Structure: CH₂Br–CBr(CH₃)₂ (derived from CH₂=C(CH₃)₂ + Br₂)
IUPAC name: 1,2-dibromo-2-methylpropane

Tetramethylene dibromide
Structure: Br–(CH₂)₄–Br
IUPAC name: 1,4-dibromobutane

Which is a better nucleophile in aqueous solution?

• In water (a protic solvent), small, highly basic ions like RO⁻ are strongly solvated by hydrogen bonding.
• Larger, less basic ions like RS⁻ are less solvated and therefore more available to attack electrophiles.

Answer: RS⁻ is the better nucleophile in aqueous solution.

Which is a better nucleophile in DMSO?

• DMSO is a polar aprotic solvent — it does not strongly solvate anions.
• Hence, nucleophilicity parallels basicity in aprotic solvents.
• Since RO⁻ is the stronger base, it is also the stronger nucleophile in DMSO.

Answer: RO⁻ is the better nucleophile in DMSO.

a. Br⁻ or Cl⁻ in H₂O → Br⁻

• In protic solvents larger, more polarizable anions are less strongly solvated and therefore better nucleophiles: I⁻ > Br⁻ > Cl⁻ > F⁻.

b. Br⁻ or Cl⁻ in DMSO → Cl⁻

• In polar aprotic solvents nucleophilicity follows basicity (smaller, harder = better): Cl⁻ is a better nucleophile than Br⁻ in DMSO.

c. CH₃O⁻ or CH₃OH in H₂O → CH₃O⁻

• The anion (methoxide) is far more nucleophilic than neutral methanol, even though it is somewhat solvated in water.

d. CH₃O⁻ or CH₃OH in DMSO → CH₃O⁻

• In a polar aprotic solvent the anionic nucleophile is even more reactive (less solvated), so methoxide wins by a larger margin.

e. HO⁻ or ⁻NH₂ in H₂O → HO⁻

• Practical point: ⁻NH₂ is so basic that it is protonated by water (it doesn’t exist appreciably in aqueous solution), so hydroxide is the available nucleophile.

f. HO⁻ or ⁻NH₂ in DMSO → ⁻NH₂

• In an aprotic medium where ⁻NH₂ can exist, the stronger base (⁻NH₂) is the stronger nucleophile.

g. I⁻ or Br⁻ in H₂O → I⁻

• Same protic-solvent rule: the larger, more polarizable I⁻ is less solvated and therefore the better nucleophile in water.

h. I⁻ or Br⁻ in DMSO → Br⁻

• In polar aprotic solvents nucleophilicity follows basicity/charge density: the smaller Br⁻ is the stronger nucleophile than I⁻.

When you first look at alcohols (ROH) and thiols (RSH), they seem quite similar — both contain a hydrogen attached to a group 16 element (oxygen or sulfur).
Yet, when it comes to acidity, thiols clearly win.
In this post, we’ll explore why thiols (RSH) are stronger acids than alcohols (ROH) — step by step.

Step 1: Acid strength depends on conjugate base stability

The strength of an acid depends on how stable its conjugate base is after losing a proton (H⁺).

• Alcohols (ROH) lose H⁺ to form alkoxide ions (RO⁻)
• Thiols (RSH) lose H⁺ to form thiolate ions (RS⁻)

The more stable the conjugate base, the stronger the acid.

So, we must compare the stability of RO⁻ and RS⁻.

Step 2: The role of atom size and polarizability

Sulfur (S) is larger and more polarizable than oxygen (O).
That means the negative charge on sulfur in RS⁻ is spread over a larger volume, making it more stable.

In contrast, oxygen is smaller and holds the negative charge tightly on a small area, creating stronger charge density and less stability.

Result: RS⁻ is more stable than RO⁻ → RSH is a stronger acid.

Step 3: Bond strength difference

The S–H bond is weaker than the O–H bond.
It takes less energy to break the S–H bond and release a proton.

Weaker bond → easier H⁺ release → stronger acid

Step 4: Electronegativity vs Polarizability

Although oxygen is more electronegative than sulfur, electronegativity isn’t the main factor here.
For acid strength, charge delocalization and bond strength dominate — and sulfur’s large, polarizable nature stabilizes the anion far better than oxygen.

tep 5: pKa values tell the story

A lower pKa means a stronger acid — so thiols are clearly more acidic than alcohols.

✅ Final Summary

Conclusion

Thiols (RSH) are stronger acids than alcohols (ROH) because their conjugate bases (RS⁻) are more stable.
Sulfur’s larger size and greater polarizability allow the negative charge to spread out, and the weaker S–H bond makes proton loss easier.
So, while oxygen wins in electronegativity, sulfur wins in stability, making RSH the stronger acid overall.

A carbene is a highly reactive organic species in which a carbon atom has only six valence electrons (instead of the usual eight) and is bonded to two substituents.

General Features:

• General formula: R₂C:
• Structure: Carbon in carbene is divalent (forms 2 bonds).
• Electron deficiency: Only 6 valence electrons → makes carbenes very reactive.
• Bond angle: Usually about 104–150°, depending on type.

Types of Carbenes:

1. Singlet carbene
   • Both non-bonded electrons are paired in the same orbital.
   • Usually bent structure (~104° bond angle).
   • Electrophilic (electron-loving).
2. Triplet carbene
   • The two non-bonded electrons occupy different orbitals with parallel spins.
   • Linear or nearly linear structure (~130–150° bond angle).
   • More stable than singlet.

Examples:

• Methylene (:CH₂) → simplest carbene.
• Dichlorocarbene (:CCl₂) → formed in Reimer–Tiemann reaction.

Preparation:

• By photolysis or pyrolysis of diazo compounds (e.g., CH₂N₂ → :CH₂ + N₂).
• By decomposition of haloforms (CHCl₃ + base → :CCl₂).

Reactivity:

• Carbenes add to double bonds → form cyclopropanes.
• Insert into C–H bonds.
• Highly reactive intermediates in organic chemistr

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed in the process. Catalysts work by facilitating the formation of the transition state, enabling the reaction to proceed more rapidly. They remain unchanged chemically and are not consumed during the reaction, allowing them to participate in multiple reaction cycles.

Two examples of catalysts are:

1. Enzymes: Enzymes are biological catalysts that facilitate and regulate biochemical reactions in living organisms. They are typically proteins that act as catalysts by lowering the activation energy required for specific reactions. Enzymes play a crucial role in various biological processes such as digestion, metabolism, and DNA replication. For example, the enzyme amylase catalyzes the hydrolysis of starch into smaller sugar molecules.
2. Platinum in Catalytic Converters: Platinum and other precious metals (such as palladium and rhodium) are commonly used as catalysts in catalytic converters of automobiles. They facilitate the conversion of harmful pollutants from exhaust gases into less harmful substances. For instance, platinum catalysts help to convert carbon monoxide (CO) into carbon dioxide (CO2) and nitrogen oxides (NOx) into nitrogen (N2) and oxygen (O2), reducing their environmental impact.

These examples demonstrate how catalysts can significantly enhance reaction rates and enable chemical transformations without being consumed in the process, making them crucial in various industrial, environmental, and biological applications.

Adsorption and absorption are two distinct processes that involve the interaction of substances with a solid or liquid surface. Here are the key differences between adsorption and absorption:

1. Nature of Interaction:

• Adsorption: Adsorption refers to the adherence or accumulation of atoms, ions, or molecules from a gas or liquid phase onto the surface of a solid or liquid. It involves weak intermolecular forces of attraction between the adsorbate and the adsorbent. The adsorbate remains on the surface without penetrating or entering the interior of the adsorbent material.
• Absorption: Absorption involves the penetration or uptake of a substance (liquid or gas) into the bulk of a solid or liquid material. The absorbed substance disperses within the absorbing material, entering its interior or matrix. Absorption can involve dissolution of the absorbed substance in the absorbing material.

2. Surface Area:

• Adsorption: Adsorption occurs specifically at the surface of the adsorbent material, taking place only on the exposed surface area. The concentration of the adsorbate is generally higher at the surface compared to the bulk.
• Absorption: Absorption occurs throughout the bulk of the absorbing material, not limited to the surface area. The absorbed substance permeates or disperses within the absorbing material.

3. Reversibility:

• Adsorption: Adsorption is typically a reversible process, meaning that the adsorbate can be desorbed or removed from the surface under suitable conditions, such as changes in temperature or pressure.
• Absorption: Absorption is not necessarily a reversible process. The absorbed substance may remain within the bulk of the absorbing material and might not be easily released.

4. Energy Involved:

• Adsorption: Adsorption generally involves weak intermolecular forces (such as van der Waals forces) between the adsorbate and the adsorbent. The energy associated with adsorption is lower than that of chemical bonds.
• Absorption: Absorption often involves stronger interactions, such as chemical bonds or intermolecular forces, between the absorbed substance and the absorbing material. The energy associated with absorption is generally higher than that of adsorption.

In summary, adsorption refers to the adherence of substances onto a surface, occurring at the surface and involving weak intermolecular forces. Absorption, on the other hand, involves the penetration of substances into the bulk of a material, occurring throughout the material and often involving stronger interactions.

In chemistry, adsorption refers to the process by which atoms, ions, or molecules from a gas or liquid phase adhere to the surface of a solid or liquid substance. This phenomenon involves the accumulation of the adsorbate (the substance being adsorbed) at the interface between the adsorbent (the surface to which adsorption occurs) and the fluid phase.

Adsorption is a surface phenomenon and can occur due to various intermolecular forces, such as van der Waals forces, electrostatic interactions, and hydrogen bonding. The adsorption process is typically reversible, meaning that adsorbate molecules can detach from the surface under suitable conditions, such as changes in temperature or pressure.

Adsorption is classified into two main types based on the strength of the interaction between the adsorbate and the adsorbent:

1. Physical Adsorption (Physisorption): Also known as van der Waals adsorption, physical adsorption involves the weak intermolecular forces of attraction between the adsorbate and the adsorbent. These forces include London dispersion forces, dipole-dipole interactions, and induced dipole interactions. Physisorption typically occurs at relatively low temperatures and can be reversed by altering the conditions, such as increasing temperature or reducing pressure.
2. Chemical Adsorption (Chemisorption): Chemisorption involves the formation of chemical bonds between the adsorbate and the adsorbent surface. This type of adsorption is characterized by stronger interactions compared to physical adsorption. Chemisorption is specific and typically occurs at higher temperatures. The adsorption process involves the breaking of existing bonds on the adsorbate and the formation of new chemical bonds with the adsorbent surface. Chemisorption is generally not easily reversible.

Both physical and chemical adsorption play important roles in various chemical, biological, and industrial processes. Adsorption processes are utilized in applications such as gas separation, catalysis, purification, and wastewater treatment. Understanding adsorption is crucial in areas like surface science, materials science, and heterogeneous catalysis.