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Showing posts with label BACK BONDING. Show all posts
Showing posts with label BACK BONDING. Show all posts

Friday, August 6, 2021

Why Back bonding does not take place in P(SiH3)3 instead of phosphorus has lone pair and Silicon has vacant d-orbital but in N(SiH3)3 molecule back bonding does take place?

Conditions for back bonding:

(1) Both of the atoms bonded with back Bonding are must be present in 2nd-2nd or 2nd-3rd period. 4rth period onward back bonding does not take place.

(2) One of the atoms has lone pair (donor atom) and another (acceptor atom) have vacant Orbital and direction of back Bonding depends upon vacant Orbital.

(3) The donor atom must have localized donatable electron pair and there should be inter electronic repulsion (smaller size). In general these are later half second period P - block elements (F, O, N and C).

(4) The acceptor atom must have low energy empty orbital which generally are np or nd orbitals. Small and similar size orbital’s favour overlap.

(5) Back bonding is a weak pi bond thus only effective overlapping will be form back bonding.

(6) Back bonding is found to be effective and considerable in following type of overlapping.

 (i) 2p-2p

(ii) 2p-3p

(iii) 2p-3d 

(7) The extent of overlapping order is [2p-2p> 2p-3d >2p-3p]

(8) dx2-y2 and dx2 Orbital’s does not participate in back Bonding. 

Solution:

In case of  trisilyl phosphine [P(SiH3)3]  Phosphorous (P) being larger in atomic size so it does not face much interelectronic repulsion and so, not much eager to donate it’s loan pair electron and comfortable with it. So, it will not donate to Si atom in this case. Thus, back bonding will not take place in trisilyl phosphine [P(SiCH3)3].

But in the case of trisilyl amine [N(SiH3)3], the nitrogen (N) atom is smaller in atomic size leading to high interelectronic repulsion, so it wants ease by donating it’s loan pair electron to other atoms near to it. And Si has vacant d-orbital, so needy for it. Since both conditions are follow here,  hence back bonding will take place.

 Related Questions:

(1) Why trimethylamine amine ( N(CH3)3) is tetrahedral while trisilyl amine (N(SiH3)3) planner.?









Tuesday, January 5, 2021

What is/are correct statement about Boroxine ion (B3O6-3) and Borazole (Inorganic Benzene)/ B3N3H6?

 (A) Both are planer and non polar

(B) Both have aromatic character

(C) Both have ppi-ppi bond formed by pairing of unpaired electrons

(D) Electrophilic subtitution  reaction occurs at B3N3H6

SOLUTION:( A,B,D) In Boraxine ion boron and oxygen atom alternatively combined to form six member ring and also each boron atom linked with extra oxygen atoms. Both boron and oxygen atoms have sp2 hybridization (by Back bonding and all oxygen atom involved in back bonding) and planer structure due to fact ring become aromatic but due to sp3 hybrisation of oxygen atom molecule become polar.


In Borazine (Inorganic Benzene) molecule, nitrogen is more electro negative than the boron. Nitrogen acquires partial negative charge and boron acquires partial positive charge and back bonding take place between boron and nitrogen.

Even though Borazine and Benzene have same stricture their chemical properties are different.

(1) Organic benzene is C6H6 while Inorganic benzene is Borazine having chemical formula B3N3H6

(2) Borazine is more reactive than Benzene with repect to electrophic addition reactions  due to high polarity (B-N polar bond) of Borazine plecules.

(3) Aromaticity of borazine is less than benzene  hence it is less reactive  toward Eectrophilic  substitution reactions than Benzene. 

Hence options (A), (B) and (D) is correct  But Option (C) is Incorrect Both have  pi-bond due to back bonding not due to formed by pairing of unpaired electrons

 Related Questions: 

Why aqueous solution of AlCl3 is acidic in nature ?

What happen when aq AlCl3 react with Acid or Base?

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Why BF3 do not exist as dimer?. Explain.

Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

When B2H6 is allowed to react with following Lewis bases, then how may given Lewis base form adduct through symmetrical Cleavage of B2H6.

What is product of reaction between diborane (B2H6) and ammmonia (NH3)?

Why methylation of Diborane (B2H6) replace four hydrogen only ?

What is Use of Boric Acid?

What is use of Orthoboric acids?

What is basicity of "Boric acid" ?

Why Boric acid exist in solid state ?

What is structure of solid Ortho Boric acid ?

What is effect of heat on Borax?

What is the structure of trimetaboric acid and trimetaborate ion?

What is the Sodium per borate ,give the structure and its uses?

Why aqueous solution of borax reacts with two moles of acids ?

What is the molecular formula of Borax ?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

Why Borazine (B3N3H6) is also known as inorganic benzene ?.

Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

What is the difference between the structure of AlCl3 and diborane?

Sunday, December 27, 2020

Why is BCl3 a strongerLewis acid than BF3 ?

The strength of a Lewis acid is a measure of its ability to attract a pair of electrons on a molecule that is behaving as a Lewis base. Fluorine is more electronegative than chlorine, so it appears that three fluorine atoms should withdraw electron density from the boron atom, leaving it more positive.This would also happen to some extent when the peripheral atoms are chlorine, but chlorine is less electronegative than fluorine. On this basis, we would expect BF3 to be a stronger Lewis acid. However,in the BF3 molecule, the boron atom uses sp2 hybrid orbitals, which leaves one empty 2p orbital that is perpendicular to the plane of the molecule. The fluorine atoms have filled 2p orbitals that can overlap with the empty 2p orbital on the boron atom to give some double bond character (Back Bond) to the B–F bonds.

 


As a result of the contribution by resonance structures having some double bond character, the boron atom in BF3 is not as electron deficient as it is in BCl3. And hence BCl3 a stronger Lewis acid than BF3

What are the characteristics features of π-bond ?

(1) π-bond fired by lateral (sidewise) overlapping of atomic orbitals.

(2) lateral overlapping is only partial, so bonds formed are weaker and hence more reactive than sigma bond.

(3) Free rotation about a π- bond is not possible.

(4) π- bond is weaker than sigma bond.

(5) π-bonds are non directional, so do not determine the shape of a molecules.

(5) π- bond take part in resonance.

(6) π- bond formed by pure or anhybrid orbitals.


Saturday, December 26, 2020

Which orbital has much overlap capacity?

When internuclear distance is fixed then overlapping extent of atomic orbitals depends on directional nature of orbitals. And higher the directional nature of orbitals more stronger will be extent of overlapping and more stronger bond will form
Order of extent of over lapping given as:
          2p-2p > 2s-2p > 2s-2s

Why the extent of overlap is more in 2p-3d than 2p-3p?

The order of overlapping strength of orbitals is given as:

2pπ-2pπ>2pπ-3dπ>2pπ-3pπ>3pπ-3pπ.
The strength of π-bond is directly proportional to the overlapping strength of orbitals because on greater overlapping distance between two nuclei decreases and bond strength increase hence order of π-bond also given as:

2pπ-2pπ>2pπ-3dπ>2pπ-3pπ>3pπ-3pπ.

2pπ-2pπ, π-bonding is stronger than 2pπ-3dπ, π-bonding due to the lower energy gap (n=2) between them.
The importance comparison is in between 2pπ-3dπ and 2pπ-3pπ. The overlapping strength of 2pπ-3dπ  is more than 2pπ-3pπ this is due to fact that , the 3d orbitals have two lobes which are more bent than 3p orbitals. That why overlapping strength increase.

Friday, December 25, 2020

How to determine order of bond angle of Me-O-Me, H3Si-O-SiH3 and (ph)3Si-O-Si(Ph) ?

 (1) Oxygen of Me-O-Me is sp3 hybridised so C-O-C bond angle is more than 109’28” approx 110” due to crowding of methyl group.

(2) In disilyl ether , oxygen is Sp2 hybridised and planer due to back bonding between oxygen and silicon atom.  In this back bonding lone pair of oxygen atom donate to the vacant d orbital of silicon atom  due to this fact bond lengths of Si-O is decrease and  increases (approx 140”).

(3) In (Ph)3Si-O-Si(Ph)3  compounds Si-O-Si bond angle is Approx 180 due to back bonding and hybridisation is Sp.


Related Questions:

Why trimethylamine amine ( N(CH3)3) is tetrahedral while trisilyl amine (N(SiH3)3) planner.?









How to compared bond angle (C-N-C) and (Si-N-Si) in trimethyl amine and trisilyl amine respectively?

Nitrogen (N) atom in trimethyl amine [N(CH3)3] is sp3 hybridised and tetrahedral ( bond angle ~107)  due to non bonding electron pair of N is localised (more basic). On the other hand N atom of trisilyl amine [N(SiH3)3] is sp2 hybridised and trigonal planner (bond angle~120).This is due to the participation of non-bondlng pair of N into pπ-dπ back banding. Due to this delocalization of non-bonding electron pair of N in trisilyl amine it is also less basic

Related Questions:

Why trimethylamine amine ( N(CH3)3) is tetrahedral while trisilyl amine (N(SiH3)3) planner.?









What is structure (CF3)2-Al-O-Al-(CF3)2 and also find the number of pi bond or Back bond?

Thursday, December 24, 2020

What is structure (CF3)2-Al-O-Al-(CF3)2 and also find the number of pi bond or Back bond?

Generally neutral atom donates only one lone pair to back bonding because after that, electron density on that atom itself highly reduced but the compound [(CF3)2-Al-O-Al-(CF3)2] is a rare example of two lone pair donation.

Related Questions:

Why trimethylamine amine ( N(CH3)3) is tetrahedral while trisilyl amine (N(SiH3)3) planner.?









What are the structure of (1) N(SiH3)3 (2) {(Me)3Si}2N-Si(Me)3 (3) HN(SiH3)2 and give the Answers of following questions?

 

Q (1): which is greater x or y?
Q (2): which is greater x or z?
Q (3): which have greater extent of back Bonding?

SOLUTION:

Ans: (1): ‘y’ is greater than ‘x’ because of steric repulsion of -CH3 group.

Ans: (2): “z’ will be greater because one lone pair going two places.

Ans; (3): the extant of back bonding is 3rd >1st > 2nd 

Which of the following is correct order of (B-O) bond length of following compounds? (1) B(OH)3 (2) B(OMe)3 and (3) B(Me)2OH

 SOLUTION:


Extent Back Bonding is   3>1>2 and bond length order is  y>x>z  

Related Questions:

Which of the following correct statement about structure of Ortho boric acid (H3BO3 ) is/are? Statements are as

(1) Angle O-B-O =120   

(2) Angle H-O-B >109 

(3) Hybridization of atom O close to spand   

(4) Molecule is non planer and non polar

Answer: Statement (4) is wrong because molecule is planer and polar


Related Questions:

Monday, December 21, 2020

Why trimethylamine amine ( N(CH3)3) is tetrahedral while trisilyl amine (N(SiH3)3) planner.?


Nitrogen (N) atom in trimethylamine [N(CH3)3] is sp3 hybridised and tetrahedral due to non bonding electron pair of N is localised (more basic). On the other hand N atom of trisilylamine [N(SiH3)3] is sp2 hybridised and trigonal planner.This is due to the participatlon of non-bondlng pair of N into pπ-dπ back banding. Due to this delocalization of non-bonding electron pair of N in trisilylamine it is also less basic.

What is the Si–N–C bond angle in Silyl isothiocyanate and methyl isothiocyanate (H3CNCS)?

The hybridization of Nitrogen in Methyl isothiocyanate (H3CNCS) is Sp2. Thus bond angle (< C-N-C) is expected to be 120°. But it is slightly greater than 120° due to resonating structure. The resonating structure has N as Sp hybridized. Hence bond angle of the overall structure is found to be about 142°

But in case Silyl isothiocyanate (SiH3NCO), the structure is found to be (sp hybridized) 

What are the order of extent back bonding, Lewis acid character and nucleophilicity of (BF3, BCl3, BBr3, BI3)boron trihalides?

(1) Back bonding extent in boron tri halides decreases from BF3 to BI3 because on increasing of size of p-orbital of halogens atom the strength of back bond decreases thus extent of back bonding:


(2) Lewis acid character of Boron Halides is inversely proportional to extent of back bonding because on decreasing back bonding tendency to accept lone pair from base is increases thus the order of Lewis acid character is:

Hence it is clear that BF3 is weakest Lewis acid due to stronger 2pπ-2pπ back bonding (stronger partial double bond character) in BF3 (lone pair orbital of fluorine into vacant orbital of boron) and consequently behaves as less electron deficient. The back bonding gradually decreases (From BF3 to BI3) and becomes weakest in BI3. So that BI3 become strong Lewis acid

(3) The nucleophilicity(affinity towards nucleophile/water) order is inversely proportional to the Lewis acid character thus the nucleophilicity order is:


 Related Questions: 

Why aqueous solution of AlCl3 is acidic in nature ?

What happen when aq AlCl3 react with Acid or Base?

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Why BF3 do not exist as dimer?. Explain.

Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?

When B2H6 is allowed to react with following Lewis bases, then how may given Lewis base form adduct through symmetrical Cleavage of B2H6.

What is product of reaction between diborane (B2H6) and ammmonia (NH3)?

Why methylation of Diborane (B2H6) replace four hydrogen only ?

What is Use of Boric Acid?

What is use of Orthoboric acids?

What is basicity of "Boric acid" ?

Why Boric acid exist in solid state ?

What is structure of solid Ortho Boric acid ?

What is effect of heat on Borax?

What is the structure of trimetaboric acid and trimetaborate ion?

What is the Sodium per borate ,give the structure and its uses?

Why aqueous solution of borax reacts with two moles of acids ?

What is the molecular formula of Borax ?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

Why Borazine (B3N3H6) is also known as inorganic benzene ?.

Four-center two-electron bond (4C-2e Bond): Structure of AlCl3: