Topscore ochem questions

[Decan]

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I had a few questions:

Ozonolysis of alkenes and alkynes: I know from destroyer that O3 w/ Zn and H2O will cleave alkenes to aldehydes. Also, I know that without Zn and H20, the aldehyde will be coverted to caroxylic acid. But what about alkynes? My best guess is that they will be converted to carboxylic acids regardless of Zn and H2O.

On topscore test 3, q 72, I got the question right but only because it was the only choice that kept the pentane ring intact. Shouldnt it technically be carboxylic acid since it is reacted with O3 alone?

On test 3, q 71, I got this question wrong because I marked trans 3,4 cyclohexene but the answer says its cis. Isnt one group equitorial and one axial? How can I tell the difference between cis and trans in the chair conformation?

On test 3, q 81, I read in the destroyer that adding carbons to benzene in a linear fashion would result in rearrangement...so why isnt the answer B?

Thanks in advance for the help!

 

[Decan]

anyone?

 

[Flipper405]

I think you are left with an ozonide if you omit the Zn reduction step in alkenes and two ozonides in alkynes. The Zn is used to cleave the ozonides to form the carbonyls.

 

[Mstoothlady2012]

I had a few questions:

Ozonolysis of alkenes and alkynes: I know from destroyer that O3 w/ Zn and H2O will cleave alkenes to aldehydes. Also, I know that without Zn and H20, the aldehyde will be coverted to caroxylic acid. But what about alkynes? My best guess is that they will be converted to carboxylic acids regardless of Zn and H2O.

On topscore test 3, q 72, I got the question right but only because it was the only choice that kept the pentane ring intact. Shouldnt it technically be carboxylic acid since it is reacted with O3 alone?

i know right!! i chose D as the answer because it has carboxylic group and i got it wrong! sry i cant help you with that one.

On test 3, q 71, I got this question wrong because I marked trans 3,4 cyclohexene but the answer says its cis. Isnt one group equitorial and one axial? How can I tell the difference between cis and trans in the chair conformation?

when you have 1 axial & 1 equitorial on the carbon next to each other it is always cis. Either you can memorize the table that is in chap 4 in mcmurry or you can understand the concept. I can see it through the figure that they are in the same plane hence it will be cis. memorizing the table is hard for me but you can do it if you like!

On test 3, q 81, I read in the destroyer that adding carbons to benzene in a linear fashion would result in rearrangement...so why isnt the answer B?

this one is simple... when we do acylation we add the group on the benzene ring without the Cl ofcourse. Then Zn reduces the carbonyl group to an alkane. i havnt read anything about rearrangement. Acylation always attaches the carbony carbon to the benzene. And then reduction with Zn always reduces the carbonyl carbon without messing around with any other carbons.

Thanks in advance for the help!

hope that helps! good luck

 

[Decan]

It does...except for Q 81. Take a look at q#12 in the destroyer...what's the difference between the two? Thanks!