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Chemistry Forums for Students => High School Chemistry Forum => Chemistry Olympiad and other competitions => Topic started by: T on July 18, 2015, 03:49:58 AM

Title: Movement of Electrons
Post by: T on July 18, 2015, 03:49:58 AM
Hello,

The question is what is the movement of electrons in the attached pictures.

For the first reaction:

What I think will happen is the H+ has separated from the NH3 and the OH- has bonded with the H to form H2O. Something needs to replace the OH's spot in the molecule so the NH3 will turn into NH2 and H+. The NH2 will take the OH spot while the H+ will join with the H2O to form H3O+. Is this right?

For the second reaction:

From my understanding, ethene can be hydrogenated to form ethane. However there is only 1 hydrogen available. If the double bond breaks and 1 of the carbon bonds with the hydrogen then the other carbon will not have enough electrons. Could someone give me a hint?

Thanks
Title: Re: Movement of Electrons
Post by: Dan on July 18, 2015, 04:43:29 AM
Quote from: T on July 18, 2015, 03:49:58 AM
For the first reaction:

What I think will happen is the H+ has separated from the NH3 and the OH- has bonded with the H to form H2O. Something needs to replace the OH's spot in the molecule so the NH3 will turn into NH2 and H+. The NH2 will take the OH spot while the H+ will join with the H2O to form H3O+. Is this right?

There is no H2O in this question, and there is certainly no NH2 produced. It is difficult to follow what you have written - it is better to draw (or use precise scientific terminology).

Quote
For the second reaction:

If the double bond breaks and 1 of the carbon bonds with the hydrogen then the other carbon will not have enough electrons. Could someone give me a hint?

You are correct that protonation of an alkene will leave behind an electron deficient C. Have you learnt about carbocations?
Title: Re: Movement of Electrons
Post by: T on July 18, 2015, 06:25:09 PM
Quote from: Dan on July 18, 2015, 04:43:29 AM
There is no H2O in this question, and there is certainly no NH2 produced.

Since there is no NH2 produced, would it be safe to assume that after the H+ leaves the NH3 the NH3 does nothing more in the reaction?

Quote from: Dan on July 18, 2015, 04:43:29 AM
Have you learnt about carbocations?

So I read about carbocations on this site: http://www.chemguide.co.uk/mechanisms/eladd/carbonium.html

From what I read, it is possible that the reaction could turn into CH2 - CH3. Since alkyl groups "push" away electrons then the + CH2 would turn a bit negative because of the pushing. So I gather that the answer would be
CH2 - CH3?

Thanks
Title: Re: Movement of Electrons
Post by: Dan on July 18, 2015, 06:54:38 PM
Quote from: T on July 18, 2015, 06:25:09 PM
So I gather that the answer would be
CH2 - CH3?

Check your charge balance.
Title: Re: Movement of Electrons
Post by: T on July 18, 2015, 06:56:41 PM
CH2+ - CH3?