Tag: chemistry

Questions Related to chemistry

The sigma bond energy of $C-H$ bond in $C _{2}H _{6}$ is:

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. $99\ kcal$

  2. $140\ kcal$

  3. $200\ kcal$

  4. $60\ kcal$

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Correct Option: B

In carbon-hydrogen-oxygen compounds:

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. all $O-$ to $-H$ bonds are $\pi$ bonds

  2. all $C-$ to $-H$ bonds are $\sigma $ bonds

  3. all $C-$ to $-C$ bonds are $\sigma $ and/or $\pi$ bonds

  4. all $C-$ to $-C$ bonds are $\pi$ bonds

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Correct Option: B,C

$Mg _2C _3$ reacts with water to form propyne. $C _3^{4-}$ has:

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. two sigma and two pi bonds

  2. three sigma and one pi bonds

  3. two sigma and one pi bonds

  4. two sigma and three pi bonds

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Correct Option: A
Explanation:

${ Mg } _{ 2 }{ C } _{ 3 }+{ 4H } _{ 2 }O\longrightarrow { Mg(OH) } _{ 2 }+{ C } _{ 3 }{ H } _{ 4 }$ Propyne
$ { C } _{ 3 }^{ 4- }  ion $

$\left[ C\equiv C-C \right] ^{ 4- }$
$2 \, \Pi $ Bonds
$2\,\sigma$ Bonds

Give the number of $\sigma$ and $\pi$ bonds in (i)$C^{2-} _2$ (ii)$C _3^{4-}$ and (iii)$CN^{2-} _2.$

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. (i) 2 $\sigma$, 1 $\pi$; (ii) 1 $\sigma$, 3 $\pi$; (iii) 2 $\sigma$, 2 $\pi$

  2. (i) 2 $\sigma$, 1 $\pi$; (ii) 3 $\sigma$, 1 $\pi$; (iii) 2 $\sigma$, 2 $\pi$

  3. (i) 1 $\sigma$, 2 $\pi$; (ii) 2 $\sigma$, 2 $\pi$; (iii) 2 $\sigma$, 2 $\pi$

  4. (i) 1 $\sigma$, 2 $\pi$; (ii) 3 $\sigma$, 1 $\pi$; (iii) 2 $\sigma$, 2 $\pi$

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Correct Option: C
Explanation:

$(i)^{-}\textrm{C}\equiv C^-$  one $\sigma$, two $\pi$;  (ii) $^{-}\textrm{C}\equiv C-C^{3-}$ two $\sigma$, two $\pi$;   (iii) $^{-}\textrm{N}=C=N^-$ two $\sigma$, two $\pi$
Hence option C is correct.

There is $p\pi\mbox{-}d\pi$ multiple bonding in:

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. $CS _2$

  2. $CO _2$

  3. $NO _2$

  4. $NO$

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Correct Option: A
Explanation:

In $S=C=S$, p-d multiple bonding exists.
In all other molecules, p-p multiple bonding exists.

Which of the following compound has a lowest nitrogen-nitrogen bond length?


     $N _2,  N _2H _2,  N _2F _2$.

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. $N _2$

  2. $N _2H _2$

  3. $ N _2F _2$

  4. All have equal bond length.

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Correct Option: A

Select  the incorrect statement.

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. Double bond is shorter than a single bond

  2. $\sigma$-bond is weaker than a $\pi$-bond

  3. Double bond is stronger than a single bond

  4. Covalent bond is stronger than hydrogen bond

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Correct Option: B

Which of the following has $p _{\pi}-d _{\pi}$ bonding?

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. $NO _3^-$

  2. $SO _3^{2-}$

  3. $BO _3^{3-}$

  4. $CO _3^{2-}$

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Correct Option: B
Explanation:

$p \pi-p \pi$ bonding: If there is bonding between two atoms where one atom is having one vacant orbital and another is having one lone pair of electrons, then this electron pair is donated to that respective vacant orbital. This type of bonding is called $p \pi-p \pi$   or $p \pi-d \pi$ depending on the orbital to which the electron pair is donated and from which the electron pair is donated.

In the above options $SO _3^{-2}$ forms $p \pi-p \pi$ bonding.
Hence option $B$ is correct.

Which of the following statement is not correct for sigma and pi-bonds formed between two carbon atoms?

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. A sigma bond is stronger than a pi-bond.

  2. Bond energies of sigma and pi-bonds are of the same order.

  3. Free rotation of atoms about a sigma bond is allowed but not in case of a pi-bond.

  4. A sigma bond determines the direction between carbon atoms, but a pi-bond has no primary effect in this regard.

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Correct Option: B
Explanation:

A) A sigma bond is stronger than a pi-bond. This is because sigma bond is formed by axial overlap and pi bond is formed by lateral overlap. Thus the extent of overlap is greater in sigma bond formation than in pi bond formation.
Hence, the option A is correct.
B) Bond energy of sigma bond is higher than that of pi bond as sigma bond is stronger than pi bond.
Hence, the option B is incorrect.
C) Free rotation of atoms about a sigma bond is allowed but not in case of a pi-bond. When the carbon atoms of sigma bond are rotated, the axial overlap is not affected. but in case of pi bonds, the lateral overlap will be affected.
Hence, the option C is correct.
D) A sigma bond determines the direction between carbon atoms, but a pi-bond has no primary effect in this regard. A pi bond is present only when a sigma bond is already present.
hence, the option D is correct.

In allene structure, three carbon atoms are joined by :

chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

  1. three $\sigma$- and three $\pi$-bond

  2. two $\sigma$- and one $\pi$-bond

  3. two $\sigma$- and two $\pi$ - bonds

  4. three $\pi$- bonds only

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Correct Option: C
Explanation:

 Allene is $CH _{2}\, =\, C\, =\, CH _{2}$.
The terminal carbons each form one $ \sigma$ with the central carbon. The other bond formed by the terminal carbon with the central carbon is a $\pi$ bond. Hence in total there are two $\sigma$- and two $\pi$ - bonds.