What is Cannizzaro reaction?

Aldehydes that do not have an alpha hydrogen atom undergo auto-oxidation reduction reactions when heated with concentrated or 50% NaOH or KOH solutions.

That is, half of the participating aldehydes molecules are oxidized to carboxylic acids (as sodium or potassium salt) and half are oxidized to alcohols. This auto-oxidation-reduction reaction is called Cannizzaro reaction. Cannizzaro reaction is also called disproportionation reaction.

Formaldehyde, trimethylacetaldehyde, benzaldehyde or any other aromatic aldehydes participates in the Cannizzaro reaction because of the absence of alpha hydrogen.

 Which is more covalent, AgCl, NaCl, LiCl or KCl?

In the above compounds, Cl^– anion is common for all, but cations are different. According to Fajan’s rule, the covalent character in ionic compounds depends on the size of cation, anion and charge of both the cation and anion.

Now, the cation with smaller size and high charge has higher polarizing power. That is, they cause polarization of electron charge cloud of an anion to a greater extent.

Why is Cu²⁺ ion more stable than Cu⁺ ion in aqueous solution?

Many Cu⁺ compounds are not stable in aqueous solution. These compounds undergo disproportionation reactions to form metallic copper and Cu²⁺ compounds.

 Why is phenol more acidic than aliphatic alcohols?

Phenol is acidic in nature. Because of phenol can donate proton in aqueous solution. Although, phenol is weakly acidic but phenol is more acidic than aliphatic alcohols.

The strength of acid depends on the tendency of donating proton in aqueous solution easily. It has been experimentally found that phenol can donate proton easily than aliphatic alcohols.

Consequently phenol becomes more acidic than aliphatic alcohols. The acidic properties of phenol can be explained on the basis of its resonance. The lone pair of electron on oxygen atom takes part in resonance with the π electron of benzene ring.

As a result, oxygen atom gets partial positive charge and hence it attracts O – H bonded electron towards itself. Consequently O – H bond become polar as well as weak and release H⁺ ion easily.

But in case of aliphatic alcohols no such resonance takes place. Hence O – H bond of aliphatic alcohols become stronger than the O – H bond of phenol. Therefore aliphatic alcohols have a very less tendency to donate H⁺ ion. That is, phenol becomes more acidic than aliphatic alcohols.

It has been experimentally found that phenol is about one million times more acidic than aliphatic alcohols. Phenol reacts with active metals like sodium or potassium and sodium or potassium phenoxide along with hydrogen gas.

Besides of being more acidic than aliphatic alcohol phenol reacts with caustic soda or sodium hydroxide forms sodium phenoxide salt and water. But aliphatic alcohols can’t react with metallic sodium or sodium hydroxide.

Phenol (pKa = 8-10) can turn blue litmus into red, but aliphatic alcohols (pKa = 16–20) cannot turn blue litmus into red.

Why is phenol more acidic than ethyl alcohol?

 Phenol is more acidic than ethyl alcohol. This can be explained on the basis of resonance effect and inductive effect of phenol and ethyl alcohol. The – OH group of phenol has +I effect and also +R effect. But in case of phenol +R effect dominates over +I effect.

Due to this +R effect, the lone of electron on oxygen atom takes part in the resonance with π electron of benzene ring. As a result, oxygen atom of phenol gets partial positive charge.

 Why do polar solvent and weak nucleophiles favor SN1 reaction?

Polar protic solvents, such as CH3OH, CH3CH2-OH, H2O, etc., are suitable for SN1 reactions. This is because in this type of solvent, both carbocation and halide anion gain stability. That is, polar protic solvent favor SN1 reaction mechanism.

 Why do nucleophiles always attack from backside in SN2 reactions?

The SN2 reaction occurs in one step through the backside attack. That is, in this reaction, the nucleophile attacks the carbon atom of the substrate from the opposite side of the living group.

The SN2 reaction is completed through the formation of a transition state. In the transition state, the nucleophile, the carbon and the living group are in the same straight line.

 What is carbon disulfide?

Carbon disulfide is also known as carbon bisulfide, is a neurotoxic colorless volatile liquid with chemical formula, CS₂. The IUPAC name of carbon disulfide is methane dithione.

Carbon disulfide is a colorless liquid in purest form and it is light yellow under impure state. Carbon disulfide has pure chloroform like or ether like odor.

 What is carbon black?

Carbon black material is also known as acetylene black, channel black, furnace black, lamp black, and thermal black. It is a black solid with molar mass 12.01 g/mol. The density of carbon black at 20°C is 1.8-2.1 g/cc.

What is sodium hydrogen carbonate?

Sodium hydrogen carbonate is also name as sodium bicarbonate, is a chemical compound with molecular formula, NaHCO3. It is also known as an acidic salt or bi salt, which is made from carbonic acid.

What is catenation property of carbon?

Catenation property is found in organic as well as in inorganic compounds. The catenation property mainly shows carbon element in organic chemistry.   

When two or more atoms of an element combine with each other through the covalently single bond, double bond or triple bond to form a long chain structure, then that characteristic of the elements is called catenation property.

What is chiral center or stereogenic center?

Optical isomerism:

The isomerism in which two or more compounds have same physical and chemical properties but they have different behavior towards plane polarized light, are known as optical isomerism and such type of compounds are known as optically active compounds.

Chiral centers:

When a single tetrahedral atom is attached with four different groups or atoms, then traditionally such atoms have been called chiral centers or stereogenic atoms or asymmetric atoms or stereo centers.

For example, the tetrahedral carbon atom of 2-butanol that attached with four different groups is an example of chiral center. Chiral centers are often designated by an asterisk (*) sign.

 What is ammonia water in inorganic chemistry?

Ammonia water means aqueoussolution of ammonia. Ammonia water is also known as ammonia liquor, aqueous ammonia, ammonium hydroxide, aqua ammonia, ammoniacal liquor etc.

It is symbolically expressed as NH3 (aq.) or NH4OH. Ammonia water solution has fishy and highly pungent smell.