1.4 Molecular Orbital Theory | Organic Chemistry

[@bonniehauschild1743]

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[@ChadsPrep]

Hey Bonnie! Welcome to the channel we are also glad you are here :)

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[@ChadsPrep]

Awesome M A! As long as learning occurs alongside inspiring I will be happy!

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[@ChadsPrep]

More on the way Anthony! Will be releasing the chapter 2 lessons throughout the week! Happy Studying!

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[@ChadsPrep]

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[@mayarise4242]

Molecular Orbital Theory Basics Wave Functions: Atomic orbitals are depicted as three-dimensional wave functions, which can have positive and negative regions. Overlap Types: Constructive Overlap: When wave functions overlap with the same sign (both positive or both negative), leading to amplification. Destructive Overlap: When wave functions overlap with opposite signs (one positive, one negative), leading to cancellation and the creation of nodes. Molecular Hydrogen (H₂) Example Constructive Overlap: Results in a lower energy bonding molecular orbital, where electron density is concentrated between the nuclei, stabilizing the molecule. Destructive Overlap: Results in a higher energy antibonding molecular orbital, where a node is created between the nuclei, destabilizing the molecule. MO Diagram: Illustrates the energy levels of bonding and antibonding molecular orbitals. Electrons prefer the lower energy bonding orbital. Molecular Orbital Diagrams Bonding and Antibonding Orbitals: Bonding Orbital (σ1s): Lower energy, electron density between nuclei. *Antibonding Orbital (σ1s)**: Higher energy, node between nuclei. Bond Order Calculation: Bond Order=(Number of Bonding Electrons−Number of Antibonding Electrons)/2 H₂: 2 bonding electrons, 0 antibonding electrons, bond order = 1. H₂⁻: 2 bonding electrons, 1 antibonding electron, bond order = 0.5. H₂⁺: 1 bonding electron, 0 antibonding electrons, bond order = 0.5. He₂: 2 bonding electrons, 2 antibonding electrons, bond order = 0 (does not exist). Key Concepts in Molecular Orbital Theory Highest Occupied Molecular Orbital (HOMO): The highest energy molecular orbital that contains electrons. Lowest Unoccupied Molecular Orbital (LUMO): The lowest energy molecular orbital that does not contain electrons. HOMO and LUMO: Often involved in chemical reactions, as they represent the frontier orbitals. Pi (π) Molecular Orbitals Pi Overlap: Involves the sideways overlap of p orbitals. Constructive Overlap: Creates a bonding π molecular orbital. Destructive Overlap: Creates an antibonding π* molecular orbital with an additional node. MO Diagrams for Pi Bonds: Similar principles apply as with sigma bonds, but specifically involve p orbitals.

[@DaveSmith-is6dc]

Thank you for this. Quick question: around 14:00, You erase a sigma 1s electron to demonstrate H2+, but the two contributing atoms still possess an electron each. So there are two contributing electrons, but just one electron in the molecule. What happens to the other electron?

[@Astra81]

At 21:32, could you explain why it is pi 2p? What does the number before the p mean?

[@ChadsPrep]

Hi Astra! The '2' refers to the principle quantum number...the same one that is used in electron configurations. Carbon's ground state electron configuration for example is 1s^2 2s^2 2p^2. For boron, carbon, nitrogen, oxygen, and fluorine, the valence electrons are in the 2s and 2p orbitals, so any pi molecular orbitals resulting from 'p' orbitals would be from the 2p orbitals. Move down a row on the periodic table to silicon and it would have to be a '3p' orbital instead for its valence electrons. Hope this helps!

[@jeevanpranavduraimanivel3460]

Sir at 17:15 you said that electrons from homo are the ones to be donated and at lumo electrons will be recieved, shouldn't be other way around?

[@den63]

At 19:07, since the electrons can't be in the middle where the nuclei are, where are they? Are they just floating around in the positive and negative areas as close to the nuclei as possible?

[@ChadsPrep]

yes correct, but not between the nuclei where there is a node

[@snagasubramanian1365]

Where can I have the continuation of MOT for hetro bonding and further? Thanks

[@SakeenaManzoor-u4y]

Sir time in video is 11:41 . Sir as you said that the BMO is lower in energy than original atomic orbitals then why you called it HOMO (highest energy occupied mo) even though it is lower in energy and for the anti bonding mo we are also doing opposite although it has higher energy than original atomic orbitals and you call it LUMO??

[@ChadsPrep]

Is this at a different time in the video? At the time you mention I am talking about breaking/forming bonds

[@SakeenaManzoor-u4y]

@@ChadsPrep sir l wrote the time in the video it is 11:41 . This video is about MOT

[@jeevanpranavduraimanivel3460]

Hi, about timing it is 16:31

[@charliesanter2536]

Great, and informative video! Thank you! Really good to watch in preparation for me starting my degree on the 21st.

[@ChadsPrep]

Glad you found it helpful Charlie! What degree are you pursuing?

[@charliesanter2536]

@@ChadsPrep My degree is Biological and Medicinal Chemistry, with a year of Industrial Experience. I'll be studying at Exeter University in England (currently live and was born in England myself, so not going abroad or anything). MO theory is covered in one of my modules. Again, thank you!!

[@ChadsPrep]

@@charliesanter2536 Way to get a head start! Best in your studies from across the pond!

[@charliesanter2536]

@@ChadsPrep Thank you ever so much!! 😊

[@netional5154]

I am curious how electric repulsion plays into all of this? I understand the potential energy is lower in the homo orbital because the electrons are located closer to the nuclei. But they are also located closer to each other which should increase the potential energy.

[@ChadsPrep]

Remember that repulsion between electron pairs in an orbital is minimized by up/down spin direction

[@netional5154]

@@ChadsPrep ah, I didn't know that. Thanks.

[@ChadsPrep]

ah, no problem, the half up ^ and half down arrows that I use in the boxes represents this... and for the exact reason you said, to minimise repulsion one electron spins in one direction and the other spins in the opposite (which we say as up/down)

[@skylardean4540]

Well said. Thank you.

[@ChadsPrep]

You're welcome and Thank You!

[@fredbuls3298]

So, it looks like these overlapping p orbitals are not hybrid orbitals. Does that mean that p orbitals can be involved in bonding without first hybridizing with s orbitals?

[@ChadsPrep]

For pi overlap the only orbitals you will ever see involved are unhybridized p orbitals. Now sigma overlap may involve any orbitals both hydrid and unhybridized but it is the pi overlap that is specific for p orbitals. Hope this helps!

[@fredbuls3298]

@@ChadsPrep Yes, thanks so much for answering these questions.

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Love from India

[@ChadsPrep]

Love back from U.S. Vishwas!

[@ayenewtewodros7373]

You've uncomparable knowledge. Genius

[@ChadsPrep]

Thanks for saying so, Ayenew.

[@SakeenaManzoor-u4y]

And sir according to AUF BAU principle electrons will fill lowest energy orbital first .you said that when we receive electron we put it in ABMO although it is higher in energy than BMO

[@ChadsPrep]

What time in the video?

[@SakeenaManzoor-u4y]

Sir this video at 11: 41 you are talking about how to calculate bond order but at the end of this section you are talking about HUMO and LUMO.

[@SakeenaManzoor-u4y]

​@@ChadsPrepsir the time in the video is 11: 41.

[@SakeenaManzoor-u4y]

@@ChadsPrep sir the time in the video is again 11:41 .This is also relevant to the same video.

[@SakeenaManzoor-u4y]

This question is also about MOT

[@kimAhchoo]

My god you are truly saving meeeee😢

[@ChadsPrep]

Glad the channel is helping you!

[@triple_gem_shining]

3:15 we call that the PP orbital LOL sorry couldn't help myself

[@ChadsPrep]

[@hajarelidrissi8492]

wait isn't bonding orbital lower energy? How does it receive the title of HOMO being the highest energy?

[@ChadsPrep]

In diatomic hydrogen's (H2) case there is only one occupied orbital so it automatically gets the title of HOMO, likewise there is only one unoccupied orbital which is the antibonding - that gets the title of LUMO, in other examples there will be other bonding orbitals to consider for HOMO/LUMO

[@jeanblanco3358]

Super Thank you

[@ChadsPrep]

You're very welcome!

[@alquran-alkareem2231]

If all molecular orbitals exist simultaneously and each molecular orbital possess 2 nuclei each, and 2 starting hydrogen atoms total to 2 nuclei, doesn't that mean that there are 4 nuclei present at the molecular level? and if so how is it possible that you've now gone from 2 nuclei to 4 , something which I'm trying to understand.

[@ChadsPrep]

Hello Al Quran - Al Hakeem! It is the same nuclei in either case. But the different molecular orbitals are different regions of space around those nuclei where the electrons in those orbitals are likely to be found. Hope this helps!

[@JohnDoe73736]

What a Chad

[@ChadsPrep]

Glad the channel is helping you - Happy Studying!

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[@ChadsPrep]

Thank you