# Optical Isomerism Homework

Ok, this hwk is driving me crazy. We have a sheet to do on optical isomerism, and i really cant do the last part of the question:

Its about limonene which is present in citric fruits and exhibits opitcal isomerism. Here are the mirror images:

Limonene

Now the bit I am stuck on is this:

Write the structure of a compound that is formed when 1 mole of limonene is hydrogenated by 2 moles of hydrogen molecules. Does the product exhibit optical activity?

Next part:

3kg of limonene required 866.9dm3 of hydrogen for full hydrogenation at romm temperature and pressure. What was the percentage purity of the limonene? (1 mol of hydrogen occupies 24dm3 at r.t.p)

I am completely stuck on this, so any help would be appreciated!

EDIT: here's its structure, if it helps:

Limonene
Part I

Hydrogen adds across the double bonds to saturate the molecule.

This gives CH3-C6H10-CH(CH3)2

to decide whether the product exhibits optical isomerism you have to consider its symmetry. There are no carbon atoms with four different substituents and the molecule is symmetrical overall - therefore it does not have optical isomers.

Part II

866.9dm3 of hydrogen at RTP corresponds to 866.9/24 moles of hydrogen

= 36.121 moles (3dp)

as two moles of hydrogen are needed to saturate 1 mole of limonene the number of moles of limonene present = 36.121/2 =18.060 (3dp)

Mr limonene = 140

therefore equivalent mass of limonene = 18.060 x 140 = 2528.458g

you are told that the mass used was 3000 g

so the % purity = 2528/3000 x 100 = 84.282% (3dp)
charco
Part I

Hydrogen adds across the double bonds to saturate the molecule.

This gives CH3-C6H10-CH(CH3)2

to decide whether the product exhibits optical isomerism you have to consider its symmetry. There are no carbon atoms with four different substituents and the molecule is symmetrical overall - therefore it does not have optical isomers.

Part II

866.9dm3 of hydrogen at RTP corresponds to 866.9/24 moles of hydrogen

= 36.121 moles (3dp)

as two moles of hydrogen are needed to saturate 1 mole of limonene the number of moles of limonene present = 36.121/2 =18.060 (3dp)

Mr limonene = 140

therefore equivalent mass of limonene = 18.060 x 140 = 2528.458g

you are told that the mass used was 3000 g

so the % purity = 2528/3000 x 100 = 84.282% (3dp)

OMG..I love you!!! Thank you sooo much. Here, have some rep Seriously, I had given up hope of any replies, thank you soo much!!!!!
damn u beat me to it lol...i was nicely riting it out n bam! beaten! too slow these days heh
charco
Part I

Hydrogen adds across the double bonds to saturate the molecule.

This gives CH3-C6H10-CH(CH3)2

I'm a bit confused as to how u got this? Sorry to be a pain, but i find this really hard! i get the other parts tho, so thanks again
rupalini
I'm a bit confused as to how u got this? Sorry to be a pain, but i find this really hard! i get the other parts tho, so thanks again

The structural formula of both the optical isomers of 'limonene' is:

CH3-C6H8-C(CH3)=CH2

Hydrogens are added by electrophilic addition, H+ ions are attracted to the negative charge of double bonds.

There are 2 double bonds in the compound... on in the benzene ring, which is why C6H8 is converted into C6H10 and another as shown above... where the C=CH2 is converted into CH-CH3 by electrophilic addition.

This gives you...

CH3-C6H10-CH(CH3)2

Hope this helps!
Revenged
The structural formula of both the optical isomers of 'limonene' is:

CH3-C6H8-C(CH3)=CH2

Hydrogens are added by electrophilic addition, H+ ions are attracted to the negative charge of double bonds.

There are 2 double bonds in the compound... on in the benzene ring, which is why C6H8 is converted into C6H10 and another as shown above... where the C=CH2 is converted into CH-CH3 by electrophilic addition.

This gives you...

CH3-C6H10-CH(CH3)2

Hope this helps!

it does help thanks!! Our teacher gave us this hwk without properly explaining it but thanks for clearin it up!! much appreciated