Will's Chem questions

[Will T]

Okay just a few questions about Carbon Chemistry....

1. Are ketones a terminating functional group? Why or why not?
2. An isomer is a molecule that has the same molecular formula and the same empirical formula but a different structure to another molecule? Yes or no and justification please.
3. Can bromobutane be formed when butene + hydrogen bromide undergo an addition reaction? Isn't 2-bromobutane formed instead? Or can they both be formed?

Thanks in advance.

[zvezda]

1. ketones are not terminating. they involve oxygens double bonded to a carbon that is also bonded to 2 other carbon atoms.
2. isomers are molecules with the same molecular formula but different molecular structure. eg. butane and methylpropane.
3. both are formed but there is a much higher yield of 2-bromobutane as opposed to 1-bromobutane. (98 % sure), need some clarification

[Will T]

I'm getting these from the practice SAC we got for Chem, by the way.
I'm pretty sure it was asking whether or not you can react anything after a ketone?
Like, in a reaction pathway, if you get to a ketone, you can't go any further? I think that's what it means by a 'terminating functional group'. It's got nothing to do with the definition of a ketone, which is what you supplied.
The question was, are isomers also molecules with the same empirical formula but different molecular structures? I don't see why not, if they have the same molecular they should have to have the same empirical formula (because empirical is just the lowest whole number ratio)
Cheers for 3 though, still dodgy how the question said draw all products and the answers only supplied 1-bromobutane.

[zvezda]

i think its more proper to say molecular thought because were talking about structure rather than ratios. Im pretty sure ketone is the terminating functional group, but i dont remember seeing that on the practice sac

[Aurelian]

3. both are formed but there is a much higher yield of 2-bromobutane as opposed to 1-bromobutane. (98 % sure), need some clarification

This is correct; there will be a much higher yield of 2-bromobutane than 1-bromobutane (provided that the OP means but-1-ene when he talks about "butene").

What the major product is in hydohalogenation reactions such as this one is governed by something called "Markovnikov's Rule". This rule states that in electrophilic addition reactions involving HX adding over a double bond (where X is a halogen), the H will add to the carbon which already has the most hydrogens. I like to remember it as "the rich get richer" with respect to hydrogens in these types of addition reactions.

In this case, the terminal carbon of but-1-ene has hydrogens attached to it, whereas the second carbon only has one hydrogen attached to it (draw out the structure if you want to make it obvious). As a result, the hydrogen will attach itself to the terminal carbon, and the halogen (bromine, in this case) will attach itself to the second carbon. This will give you 2-bromobutane.

You don't have to know anything about the why of this rule in VCE (actually, I don't think you need to know about the rule at all), but it has to do with the relative stability of intermediates in the reaction as it progresses.

Hope that helped! =)

[zvezda]

This is correct; there will be a much higher yield of 2-bromobutane than 1-bromobutane (provided that the OP means but-1-ene when he talks about "butene").

What the major product is in hydohalogenation reactions such as this one is governed by something called "Markovnikov's Rule". This rule states that in electrophilic addition reactions involving HX adding over a double bond (where X is a halogen), the H will add to the carbon which already has the most hydrogens. I like to remember it as "the rich get richer" with respect to hydrogens in these types of addition reactions.

In this case, the terminal carbon of but-1-ene has hydrogens attached to it, whereas the second carbon only has one hydrogen attached to it (draw out the structure if you want to make it obvious). As a result, the hydrogen will attach itself to the terminal carbon, and the halogen (bromine, in this case) will attach itself to the second carbon. This will give you 2-bromobutane.

You don't have to know anything about the why of this rule in VCE (actually, I don't think you need to know about the rule at all), but it has to do with the relative stability of intermediates in the reaction as it progresses.

Hope that helped! =)

yeah definitely has. cheers aurelian