For all those good at organic chem, i need your HELP!!

[shan1997]

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I was wondering if someone can help me with a few organic chemistry homework problems. I am having trouble with the wording, can someone break it down in words i can understand and give me some clues on how to get started???

Thanks in advance

🙁

This is the way the question was worded,

1. Many functional grous contain the carbonyl bond ( C=O ) ( carbon oxygen double pbond). The reaction at the carbonyl bond is similar BUT different from C=C. Describe how the pi electrons in C=O are similar and different from pi e- in C=C

I know that pi bonds are always the second bond made ( the sigma being the first), maybe that is a way they are similar but how are they different?

2. Allylic cation ( CH2CHCH2)+1 ismore stable than methyl cation ( CH3+). The same pattern holds for allylic vs methyll free radical and anion. Explain.

I am not understanding this one


I would appreciate any help or thoughts anyone could give me

 

[Kalel]

I think that the second question has to do with electron sharing, with the larger molecule having more electrons to spread the extra charge or missing electron around. I don't know the answer to the first one.

 

[Samoa]

You really should figure it out on your own. But here's a small hint: for the first problem, what are the bond angles? For the second problem, think about electron delocalization.

 

[Bad Mojo]

Another one-word hint: electronegativity (for the first one)

 

[ewing]

Originally posted by shan1997
I was wondering if someone can help me with a few organic chemistry homework problems. I am having trouble with the wording, can someone break it down in words i can understand and give me some clues on how to get started???

Thanks in advance

🙁

This is the way the question was worded,

1. Many functional grous contain the carbonyl bond ( C=O ) ( carbon oxygen double pbond). The reaction at the carbonyl bond is similar BUT different from C=C. Describe how the pi electrons in C=O are similar and different from pi e- in C=C

I know that pi bonds are always the second bond made ( the sigma being the first), maybe that is a way they are similar but how are they different?

2. Allylic cation ( CH2CHCH2)+1 ismore stable than methyl cation ( CH3+). The same pattern holds for allylic vs methyll free radical and anion. Explain.

I am not understanding this one


I would appreciate any help or thoughts anyone could give me

1. The carbonyl can resonate between C=O:: and C-O:::. Even though in the second case there is a negative charge on the oxygen, this is a resonance contributor because O is more electronegative than C.

2. The positive charge is stabilized by resonance, because some of the electrons from the double bond can spend some time at various ends of the molecule keeping everybody happy. The methyl cation is extremely unstable and CH4 is about the worst acid you can imagine (pKa of about 60) because there is nowhere for the positive charge to delocalize.

You really need to understand resonance contributors and stabilization. Consider buy Weeks' workbook "Pushing Electrons" if you have trouble drawing resonance structures and seeing how much they contribute.

Good luck. Orgo is fun stuff, once you get into it, you'll love it.

 

[bessybug]

Originally posted by Samoa
You really should figure it out on your own. But here's a small hint: for the first problem, what are the bond angles? For the second problem, think about electron delocalization.

WTF are you talking about? The OP question concerns only the functional group . C=O vs C=C doesn't have anything to do with bond angles.
The correct answer concerns electronegativity.

 

[fun8stuff]

Originally posted by bessybug
WTF are you talking about? The OP question concerns only the functional group . C=O vs C=C doesn't have anything to do with bond angles.
The correct answer concerns electronegativity.

perhaps this person was referring to how sigma bonds are form directly between atoms and pi bonds are actually formed at angles around the atoms- the pi bonds overlap eachother much less than the sigma. who knows... but the answer does lie in electronegativity and electron delocalization (for the first)

 

[shan1997]

thanks for all the responses ( especially ewing) i appreciate it. I just needed some direction and i am glad there are some very nice and willing people on sdn to help me out. If anyone else has any other thoughts feel free. Thanks again

 

[LP1CW]

What am I missing? This question is straight forward. Skim the chapter and you'll find the answer. It's not even close to tricky.

 

[Noeljan]

Hey shan,
I think you need to go over some basics about electroneg, bonding, hybridization, etc. Maybe even some general chem type review book before trying to solve any further problems. PM me if you need any more help.
J