Random organic chemistry questions

[badmintondr]

1. What exactly do I need to know about anti-molecular binding orbitals?...Is this saying something about anti-spins (non-parallel)..?

2. What is the reasoning as to why a more substituted single bond has lower bond strength?



3. For Lewis structures, I know there are preferences for HONC (1,2,3,4) (Also that atoms with d orbitals can make mroe than 4 bonds) but aside from that, is the number of bonds typically made given by the electrons needed to make an octet?

Na-1, Ca-2, B-3, C-4, N-3, O-2, Cl-1 (Is this right?)

I'm not truly and intuitively understanding how many bonds atoms with d orbitals should be making.

Thanks

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[ThirdEye]

1. What exactly do I need to know about anti-molecular binding orbitals?...Is this saying something about anti-spins (non-parallel)..?

2. What is the reasoning as to why a more substituted single bond has lower bond strength?



3. For Lewis structures, I know there are preferences for HONC (1,2,3,4) (Also that atoms with d orbitals can make mroe than 4 bonds) but aside from that, is the number of bonds typically made given by the electrons needed to make an octet?

Na-1, Ca-2, B-3, C-4, N-3, O-2, Cl-1 (Is this right?)

I'm not truly and intuitively understanding how many bonds atoms with d orbitals should be making.

Thanks

1) No idea
2) More substitutions pull e- away from the atoms, weakening the other bonds.
3)Yes, except for B, S, and P (I believe). B typically likes 3 bonds and I don't really remember the other exceptions right now.


I don't think the MCAT will throw transition metals at you if they ask about lewis structures.

 

[unique135]

1. I don't know how would be required to know but here's the basics.

Bonding Orbitals (BO): Molecular orbitals in which electrons are found between nuclei.
Antibonding Orbitals (AO): Molecular orbitals in which electrons are NOT found between nuclei.

• Every molecular orbital has AO and BO.
• Energy level of AO is greater than that of BO.
• Order of filling: AO(s-orbital), BO (s), AO (p-orbital), BO (p),...(Building-up principle)
• Bond length (Number of bonds existing) = 1/2 (electron in AO + electron BO)

It is best to look at few common examples such H2, He2 and NO.


2. Let me know if I am wrong.

Anything that messes with the center of negative charge (including those overlapping of bonds). In this context, it could be

a. Inductive effect: Presence of electron donating/withdrawing groups. Electron withdrawing groups will stabilize the bond**.

b. Steric hindrance: More substituted single bond will place the molecule at high energy level. Thus, the molecule easily reacts because of lower stability >> less overlapping of bond >> less bond strength. Common example of conformers of butane through Newman projections.



3. Octet rule is good for 2nd and 3rd periods. After that, it is doesn't work (atleast for me). Even in 2nd and 3rd periods, there are exceptions.

Some Exceptions for Octet Rule:
a. Molecules with odd number of electrons
Example: NO (Number of electrons are 11)
b. Molecules with electrons less than octet
Examples: Boron (BF3 - six electrons only)
Beryllium (BeCl2 - four electrons)
Mostly Group IIA and IIIA (B, Be, Al)
c. Molecules with electrons more than octet
Example: Phosphorous pentafluoride (using empty 3d orbitals)

 

[ieatkimbap]

2. Let me know if I am wrong.

Anything that messes with the center of negative charge (including those overlapping of bonds). In this context, it could be

a. Inductive effect: Presence of electron donating/withdrawing groups. Electron withdrawing groups will stabilize the bond**.

b. Steric hindrance: More substituted single bond will place the molecule at high energy level. Thus, the molecule easily reacts because of lower stability >> less overlapping of bond >> less bond strength. Common example of conformers of butane through Newman projections.

I agree to this reasoning to some extent but I have a different reason as to why a more substituted single bond have lower bond strength.

When you are considering a more substituted molecule and you're analyzing bond strength, look at the hybridizations on the carbons of interest (assuming we're taking about organic chemistry). An sp3 carbon (more substituted) will have less "s character" contributing to formation of a sigma bond than a sp carbon.

Hope this makes sense!