[Omega909]

This question has been driving me absolutely nuts. Here it is written exactly:

An alkene "X" with molecular formula C₇H₁₂ adds HBr to give a SINGLE alkyl halide "Y" with molecular formula C₇H₁₃Br and undergoes catalytic hydrogenation to give 1,1-dimethylcyclopentane. Draw the structures of "X" and "Y"

What I've deduced so far:

the alkene X has two double bonds since it has 2 degrees of unsaturation.

the alkyl halide Y has one double bond and a Br and H went onto the carbons that used to have a double bond.

Since the product of the catalytic reaction is a cyclopentANE rather than a cyclopentene, that means that the remaining double bond has been broken. However, in the name of the cyclopenetane, the Br is not denoted anywhere which leads me to believe that it was removed somehow.

Also, the question does not specify if the alkene X must be a cycloalkene and I'm unsure of the mechanisms that would need to occur to turn an Alkene into a Cycloalkene/cycloalkane.

While I would obviously appreciate the answer to this question, I would definitely appreciate a breakdown of how this works more.

Thank you kindly!

[phth]

Markonikov's rule predicts the thermodynamic(major product) under most cases.  what isomer produces the same kinetic and thermodynamic product?

[mjc123]

Does "degree of unsaturation" always imply "double bond"? If there are 2 double bonds, why does only one HBr add? If the product of hydrogenation is a cycloalkane, what does that suggest?
And it is X that is hydrogenated, not Y - there is no need to remove bromine.

[Omega909]

Does "degree of unsaturation" always imply "double bond"? If there are 2 double bonds, why does only one HBr add? If the product of hydrogenation is a cycloalkane, what does that suggest?
And it is X that is hydrogenated, not Y - there is no need to remove bromine.

To my knowledge I thought the degree of unsaturation with regards to Arenes implied the number of double bonds that occur.

As the product of hydrogenation is a cycloalkane, one would be lead to believe that the reactant was a cycloalkene.

So even though the degree of unsaturation is 2, there isn't necessarily two double bonds?

[Omega909]

Does "degree of unsaturation" always imply "double bond"? If there are 2 double bonds, why does only one HBr add? If the product of hydrogenation is a cycloalkane, what does that suggest?
And it is X that is hydrogenated, not Y - there is no need to remove bromine.

To my knowledge I thought the degree of unsaturation with regards to Arenes implied the number of double bonds that occur.

As the product of hydrogenation is a cycloalkane, one would be lead to believe that the reactant was a cycloalkene.

So even though the degree of unsaturation is 2, there isn't necessarily two double bonds?

Edit: After using the info you gave me and doing more research, I've concluded that X is 3,3-dimethylcyclopent-1-ene and Y is 3-bromo-1,1-dimethylcyclopentane

[mjc123]

A cycloalkane has 2 fewer H atoms than the corresponding linear alkane, e.g. cyclohexane C₆H₁₂ and hexane C₆H₁₄. Of course hexene is also C₆H₁₂. Thus "degree of unsaturation" calculated from the C:H ratio may include rings as well as double or triple bonds. However, a cycloalkane is saturated in the sense that it does not undergo the typical reactions of double bonds, e.g. addition of HBr. So X has 2 units of unsaturation, but only adds one HBr - a cycloalkene would fit the bill.

[sjb]

Edit: After using the info you gave me and doing more research, I've concluded that X is 3,3-dimethylcyclopent-1-ene and Y is 3-bromo-1,1-dimethylcyclopentane

Check your names but I think you're on the right track

[Dan]

To my knowledge I thought the degree of unsaturation with regards to Arenes implied the number of double bonds that occur.

No, but in any case there are no arenes (= aromatic hydrocarbon) anywhere in this question.