Alcohols, isomers etc.

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Sophie.cerys
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I'm really stuck on this question, any help would be really appreciated! I'm stuck on part iv - i think I've done all the other parts correctly. Thanks!


(b) Four unsaturated isomeric hydrocarbons have a relative a relative molecular mass of 56 and the following percentage composition by mass: C, 85.7%; H, 14.3%. These four isomeric hydrocarbons can be made to react with steam forming alcohols. One of the alcohols, T, does not react with acidified potassium dichromate(IV) K2Cr2O7.

(i) Calculate the molecular formula of the four isomers.​ ​ [3]

(ii) Deduce the structure of the four isomers.​ ​ [4]

(iii) Deduce all the alcohols that could be formed from the four isomers. ​ ​ [4]

(IV) Identify the alcohol T and deduce which of the isomers in (b)(ii) reacted with steam to produce it.




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Gerry-Atricks
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(Original post by Sophie.cerys)
I'm really stuck on this question, any help would be really appreciated! I'm stuck on part iv - i think I've done all the other parts correctly. Thanks!


(b) Four unsaturated isomeric hydrocarbons have a relative a relative molecular mass of 56 and the following percentage composition by mass: C, 85.7%; H, 14.3%. These four isomeric hydrocarbons can be made to react with steam forming alcohols. One of the alcohols, T, does not react with acidified potassium dichromate(IV) K2Cr2O7.

(i) Calculate the molecular formula of the four isomers.​ ​ [3]

(ii) Deduce the structure of the four isomers.​ ​ [4]

(iii) Deduce all the alcohols that could be formed from the four isomers. ​ ​ [4]

(IV) Identify the alcohol T and deduce which of the isomers in (b)(ii) reacted with steam to produce it.




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What kind of alcohols dont react with acidified potassium dichromate?
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Dark768
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So you know the percentage composition and with this you can find the empirical formula. Then you can find out the molecular formula by matching it with the molecular mass. After you can draw out the different isomers because you'll know the number of C and H atoms in the molecule. One of the isomers will form a secondary or tertiary alcohol as it doesn't react with acidified dichromate to form an aldehyde.
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Gerry-Atricks
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(Original post by Dark768)
So you know the percentage composition and with this you can find the empirical formula. Then you can find out the molecular formula by matching it with the molecular mass. After you can draw out the different isomers because you'll know the number of C and H atoms in the molecule. One of the isomers will form a secondary or tertiary alcohol as it doesn't react with acidified dichromate to form an aldehyde.
No,secondary alcohols oxidise to ketones, it must be a tertiary alcohol-she just needs to find a way to branch it that matches molecular formula
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Dark768
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(Original post by glad-he-ate-her)
No,secondary alcohols oxidise to ketones, it must be a tertiary alcohol-she just needs to find a way to branch it that matches molecular formula
Sorry, you're correct. I'm just too used to seeing acidified dichromate used to form carboxylic acids aha
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Gerry-Atricks
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(Original post by Dark768)
Sorry, you're correct. I'm just too used to seeing acidified dichromate used to form carboxylic acids aha
Thats what a2 organic does to you- you forget the AS reactions
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Dark768
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(Original post by glad-he-ate-her)
Thats what a2 organic does to you- you forget the AS reactions
aha too true, can't wait to get chem over and done with
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Gerry-Atricks
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(Original post by Dark768)
aha too true, can't wait to get chem over and done with
Yes its a stress but i need it for my course-what did you apply for?
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Dark768
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(Original post by glad-he-ate-her)
Yes its a stress but i need it for my course-what did you apply for?
I applied for medicine, yourself?
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Gerry-Atricks
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(Original post by Dark768)
I applied for medicine, yourself?
as did i, what unis?
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Dark768
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(Original post by glad-he-ate-her)
as did i, what unis?
I applied to Liverpool, Sheffield, Exeter and Plymouth and got an offer from plymouth and rejection from the rest. You?
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Gerry-Atricks
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(Original post by Dark768)
I applied to Liverpool, Sheffield, Exeter and Plymouth and got an offer from plymouth and rejection from the rest. You?
imperial, UCL, cambridge and st george`s- offer from UCL and rejected from rest- news flash medicine is competitive
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Dark768
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(Original post by glad-he-ate-her)
imperial, UCL, cambridge and st george`s- offer from UCL and rejected from rest- news flash medicine is competitive
Wayyyyy too competitive aha
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Gerry-Atricks
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(Original post by Dark768)
Wayyyyy too competitive aha
application process not good for your heart
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