Physical properties of ethers - class-XII

Ethers ROR cannot form intermolecular Hydrogen bond due to the absence of H attached with the electronegative atom as N/O/F, but in case of alcohols, they have -OH which can undergo intermolecular hydrogen bonding and that increases their boiling point.

The boiling point of a molecule depends on the strength of intermolecular interaction such as Vandewaal's attraction, hydrogen bonding etc.

Lower molecular weight ethers, such as diethyl ether, have low boiling points, making them highly volatile and flammable.

Diethyl ether (C2H5OC2H5) lacks the ability to form hydrogen bonds between its own molecules, unlike water, ethanol, and methanol, resulting in a much lower boiling point.

Boiling point of Diethyl ether $=34.6^0C$

The high boiling point of ethanol $(78.2 ^oC)$ compared to dimethyl ether $(-23.6^oC)$, though both having the same molecular formula $C _2H _6O$, is due to Hydrogen bonding.
Hydrogen bonding is observed when H atom is attached to more electronegative N, F or O atom.
Ethanol molecules are associated due to hydrogen bonding. This results in higher boiling point.
However, hydrogen bonding is not possible in dimethyl ether.

Maximum boiling point would be shown by n propanol, $\displaystyle { CH } _{ 3 }-{ CH } _{ 2 }-{ CH } _{ 2 }-OH$.
In n-propanol, the molecules are associated due to hydrogen bonding. Hence, the boiling point is higher.
In dimethyl ether and diethyl ether, the boiling point is lower as hydrogen bonding is not possible.
The extent of the hydrogen bonding in isopropanol is lower than that in n-propanol due to +I effect of two methyl groups.
Also, as the degree of branching increases, the boiling point decreases.

D
Due to less chance of hydrogen bonding less association so low boiling point

Ethanol $(C _2H _5OH)$ and dimethyl ether $(CH _3-O-CH _3)$ have same molecular formula but different functional groups, so they are isomers.

The correct option is $C$. Ethoxyethane is an ether group which is miscible to the alcohol that is Butan $-1-$ol. This is because they have the same molecular mass. 

An ether is more volatile than an alcohol having the same molecular formula. This is due to intermolecular hydrogen bonding in alcohols. In alcohols, $H$ atom is attached to electronegative $O$ atom. Due to this, $H$ atom of $-OH$ group of one alcohol molecule forms a hydrogen bond with $O$ atom of $-OH$ group of the second alcohol molecule. This results in the intermolecular association. It increases the boiling point and decreases the volatility of alcohol. Such inter-molecular hydrogen bonding is not possible in others as in ethers, H atom is not attached to an electronegative $O$ atom.

The miscibility of ether with water resembles those of alcohol of the same moleculer mass. It is generally due to the hydrogen bonding with water in alcohol. So the correct option is $B$.

The correct option is $B$. The lower number of ether is soluble in water. So dimethyl ether compound is generally soluble in water. 

In case of ether there is no intermolecular forces which results in low boiling points or high vapour pressures. Hence lower ethers are highly volatile and flammable.

The correct option is $A$. Ether is less soluble than alcohol in water because alcohol forms hydrogen bond with water molecule but ether does not.

Diethyl ether $ \displaystyle CH _3-CH _2-O-CH _2-CH _3$ and Methyl propyl ether $ \displaystyle CH _3-O-CH _2-CH _2-CH _3$ are metamers of each other. They have same molecular formula but different alkyl groups attached on either side of the oxygen atom.

Ether has least boiling point as it cannot form hydrogen bonds. Ethylene glycol, water and phenol can form intermolecular hydrogen bonds which lead to intermolecular hydrogen bonding and high boiling points. Hydrogen bonding is possible when $H$ atom is attached to electronegative $N,\ O$ or $F$ atom.

The density of ether increases gradually with increase in the molecular mass. But their density is less than 1. And we know that the density of water is 1. Hence all ethers are lighter than water.

The densities of ethers increase with increase in the molecular masses of ethers.

Ethers show metamerism. When the two compounds have same ratios of atoms but different arrangements, then they are said to show metamerism. e.g. Methyl propyl ether and diethyl ether have same ratios of carbon, hydrogen and oxygen atoms but different structural arrangements. Hence they are metamers of each other.

Ethers have general structural formula R-O-R'. Hence all of them have the C-O bond. We know that the C-O bond is polar due to the difference between the electronegativities of carbon and oxygen. Hence, ethers show dipolar nature.

The correct option is B. $R-O-R$ is generally the functional group of the ether which is non-polar and does not form hydrogen bonding. 

Ethers and alcohols are the functional isomers of each other. They have same molecular formula but different functional groups.

Benzyl alcohol (C7H8O) and anisole (methoxybenzene, C7H8O) share the same molecular formula, making them isomers.

Ethers having same molecular formula but different alkyl groups on either side of the oxygen atoms show metamerism. Ethoxy ethane and methoxypropane, phenetole and benzyl methyl ether show metamerism.

 Ethers having same molecular formula but different alkyl groups on either side of the oxygen atoms show metamerism. Ethoxy ethane and methoxypropane, phenetole and benzyl methyl ether show metamerism.

Ethers containing two or more carbon atoms show functional isomerism with alcohols. Methoxy methane and ethanol are functional isomers.

Isomers with the same molecular formula but different alkyl groups (around the functional group) are called metamers. An ether with formula $C _4H _{10}O$ has 3 metamers.

Ethers exhibit chain isomerism ,functional isomerism, Metamerism and Chain isomerism.Ethers with the same formula and having different carbon chain skeletons are called chain isomers.

The given two ethers have different carbon atoms on the two sides of a bifunctional group (-O-). Hence these are the metamers of each other.

Diethyl ether has lower density than water. The density of diethyl ether is 713 kg/m$^3$. The density of water is 1000 kg/m$^3$.
Water molecules are closer to each other than the molecules of ether. This is due to intermolecular hydrogen bonding in water which is not possible in diethyl ether.

With the increase in the molecular weight, the density of ethers increase.
For example, diethyl ether has a lower density than dibutyl ether.
The density of diethyl ether is 713 kg/m$^3$.
The density of dibutyl ether is 769 kg/m$^3$.

Diethyl ether has lower density than dibutyl ether.
The density of diethyl ether is 713 kg/m$^3$.
The density of dibutyl ether is 769 kg/m$^3$.

The isomerism exhibited by ${ C } _{ 2 }{ H } _{ 5 }O{ C } _{ 2 }{ H } _{ 5 }$ and $CH _3-O-\underset{CH _3}{\underset{|}{C}H}-CH _3$ is metamerism. They have same molecular formula but different alkyl groups on  either side of functional group.

Ethers have oxygen attached to two alkyl groups ($R-\overset { .. }{ \underset { ^{ .. } }{ O }  } -R'$). Therefore, due to the high electronegativity of oxygen, it can form hydrogen-bond with water molecules similar to alcohol. But due to the absence of $H$ on $O$ of ether, they can only act as hydrogen bond acceptor (unlike alcohols) and thus have lower solubility in water than alcohols with similar molecular weight.

An ether is more volatile than an alcohol having same molecular formula because intermolecular hydrogen bonding in alcohols. 

Thioethers (sulfides) have higher boiling points than their corresponding ethers because sulfur is larger and less electronegative than oxygen, leading to greater polarizability and stronger London dispersion forces.

Dimethyl ether (CH3-OCH3) is a gas at room temperature (bp -24 C). Ethyl methyl ether (C2H5-OCH3) has a boiling point of about 7-8 C, making it a volatile liquid at room temperature. Diethyl ether (C2H5-OC2H5) is also a liquid, but the question implies identifying a specific example.