difference between alicyclic and aromatic ?

Watch
medhelp
Badges: 14
Rep:
?
#1
Report Thread starter 4 years ago
#1
what is the difference:

alicyclic are joined to each other in a ring structure, aromatic is when some or all of the carbon atoms are found in a benzene ring.

so what is the real difference?

are aromatic hydrocarbons just alicyclic but with double bonds? and does this make them a sub-group of alicyclic hydrocarbons or is it a separate thing like aliphatic is?

and if the underlined bit is true, does that mean all alicyclic hydrocarbons with 3 double bonds are automatically aromatic?



side question: are the 3 double bonds the max amount of double bonds a carbon ring structure can have?
Spoiler:
Show
FailingChemist perhaps you can help me ?
0
reply
username1539513
Badges: 21
Rep:
?
#2
Report 4 years ago
#2
(Original post by medhelp)
what is the difference:

alicyclic are joined to each other in a ring structure, aromatic is when some or all of the carbon atoms are found in a benzene ring.

so what is the real difference?

are aromatic hydrocarbons just alicyclic but with double bonds? and does this make them a sub-group of alicyclic hydrocarbons or is it a separate thing like aliphatic is?

and if the underlined bit is true, does that mean all alicyclic hydrocarbons with 3 double bonds are automatically aromatic?



side question: are the 3 double bonds the max amount of double bonds a carbon ring structure can have?
Spoiler:
Show
FailingChemist perhaps you can help me ?
You kind of have the right idea here, the main difference between them is that in an aromatic compound such as benzene the electrons are delocalised (spread out) around all the carbon atoms within the circle. In alicyclic compounds with 3 double bonds the electrons stay within the area of the double bond. In textbooks benzene is sometimes depicted as having 3 double bonds but it's more accurate to represent it as a hexagon with a circle in the middle

You can prove this by looking at the enthalpy required to break a double bond and a single bond in cyclohexene and then compare it to breaking a bond in benzene. The enthalpy value is more than that required to break the single bond but less than the required value to break the double bond thus proving delocalisation.

Delocalisation is the reason why the chemistry of benzene is very different from the chemistry of cyclohexene. You will learn more about it in A2
1
reply
alow
Badges: 19
Rep:
?
#3
Report 4 years ago
#3
(Original post by medhelp)
what is the difference:

alicyclic are joined to each other in a ring structure, aromatic is when some or all of the carbon atoms are found in a benzene ring.

so what is the real difference?

are aromatic hydrocarbons just alicyclic but with double bonds? and does this make them a sub-group of alicyclic hydrocarbons or is it a separate thing like aliphatic is?

and if the underlined bit is true, does that mean all alicyclic hydrocarbons with 3 double bonds are automatically aromatic?



side question: are the 3 double bonds the max amount of double bonds a carbon ring structure can have?
Spoiler:
Show
FailingChemist perhaps you can help me ?
To be aromatic, a compound must satisfy three conditions:

-There must be a delocalised π-system containing 4n+2;\: n \in \mathbb{N} electrons (i.e. alternating double and single bonds).
-All electrons which contribute to the π-system must be in the same plane (i.e. no puckered rings).
-Contributing electrons must be arranged in at least one ring.

Structures such as benzene:
Image
Clearly obey these conditions.

Yes, you can have a cycle with more double bonds, such as cyclooctatetraene:
Image
However, this does not meet the requirements for aromaticity due to it's 8 electrons in a π-system. We actually call compounds with 4n;\: n \in \mathbb{N} electrons (along with the other aromaticity requirements) antiaromatic. Antiaromatic structures are incredibly unstable, meaning compounds such as cyclooctatetraene pucker out of the plane to avoid this:
Image



The structure with double bonds is almost always more useful.



Not necessarily, they just don't form an aromatic system.
1
reply
FailingChemist
Badges: 2
Rep:
?
#4
Report 4 years ago
#4
(Original post by medhelp)
what is the difference:

alicyclic are joined to each other in a ring structure, aromatic is when some or all of the carbon atoms are found in a benzene ring.

so what is the real difference?

are aromatic hydrocarbons just alicyclic but with double bonds? and does this make them a sub-group of alicyclic hydrocarbons or is it a separate thing like aliphatic is?

and if the underlined bit is true, does that mean all alicyclic hydrocarbons with 3 double bonds are automatically aromatic?



side question: are the 3 double bonds the max amount of double bonds a carbon ring structure can have?
Spoiler:
Show
FailingChemist perhaps you can help me ?
For anything A level I'm the worst person to ask, but i doubt at any point we wuld have to worry about such differentiation much at Uni, more recognising what you've got and the understanding of what you do with them.

But general advise for university.Remember that all of these diagrams are all incorrect and pure fantasy. The mechanisms, positions of the 'eletcrons' just what is going on? We can only geuss.

My freind made the jump to biochem and the quantum chemistry and MO stuffjust messed with him a bit, becasue lewis diagrams, bond type and a particle like electron were so ingrained into his brain he couldn't let it go.

Have the mindset, different theory, diffferent application and move on.
0
reply
alow
Badges: 19
Rep:
?
#5
Report 4 years ago
#5
(Original post by FailingChemist)
For anything A level I'm the worst person to ask, but i doubt at any point we wuld have to worry about such differentiation much at Uni, more recognising what you've got and the understanding of what you do with them.

But general advise for university.Remember that all of these diagrams are all incorrect and pure fantasy. The mechanisms, positions of the 'eletcrons' just what is going on? We can only geuss.

My freind made the jump to biochem and the quantum chemistry and MO stuffjust messed with him a bit, becasue lewis diagrams, bond type and a particle like electron were so ingrained into his brain he couldn't let it go.

Have the mindset, different theory, diffferent application and move on.
Oh, you will.
0
reply
FailingChemist
Badges: 2
Rep:
?
#6
Report 4 years ago
#6
(Original post by alow)
Oh, you will.
Ok then I will, take note of what this man says.
1
reply
alow
Badges: 19
Rep:
?
#7
Report 4 years ago
#7
(Original post by FailingChemist)
Ok then I will, take note of what this man says.
If you want to see a different method of finding if a compound is aromatic, Frost Circles are pretty cool (and give a bit more rationale behind the stability of aromatic and instability of anitaromatics -which it turns out are diradicals-).

http://www.chemgapedia.de/vsengine/v...ost.vscml.html
0
reply
FailingChemist
Badges: 2
Rep:
?
#8
Report 4 years ago
#8
(Original post by alow)
If you want to see a different method of finding if a compound is aromatic, Frost Circles are pretty cool (and give a bit more rationale behind the stability of aromatic and instability of anitaromatics -which it turns out are diradicals-).

http://www.chemgapedia.de/vsengine/v...ost.vscml.html
I'll be honest, I've not touched my aromatic chemistry yet, at all (but I should have). But I've got all the study materials and notes, so at some point next week, i should be up to scratch. It doesn't take long, but it does hurt the brain.

Thanks
0
reply
username1539513
Badges: 21
Rep:
?
#9
Report 4 years ago
#9
(Original post by alow)
To be aromatic, a compound must satisfy three conditions:

-There must be a delocalised π-system containing 4n+2;\: n \in \mathbb{N} electrons (i.e. alternating double and single bonds).
-All electrons which contribute to the π-system must be in the same plane (i.e. no puckered rings).
-Contributing electrons must be arranged in at least one ring.

Structures such as benzene:
Image
Clearly obey these conditions.

Yes, you can have a cycle with more double bonds, such as cyclooctatetraene:
Image
However, this does not meet the requirements for aromaticity due to it's 8 electrons in a π-system. We actually call compounds with 4n;\: n \in \mathbb{N} electrons (along with the other aromaticity requirements) antiaromatic. Antiaromatic structures are incredibly unstable, meaning compounds such as cyclooctatetraene pucker out of the plane to avoid this:
Image



The structure with double bonds is almost always more useful.



Not necessarily, they just don't form an aromatic system.
This is right but too complicated for a-level

I was answering the question from the perspective of an a-level question. You don't need to know about Huckel's Rule and all the other stuff until university
1
reply
alow
Badges: 19
Rep:
?
#10
Report 4 years ago
#10
They were asking a question which cannot be explained using A Level knowledge.

However much of your answer was wrong, even in an A Level context.
0
reply
username1539513
Badges: 21
Rep:
?
#11
Report 4 years ago
#11
(Original post by alow)
They were asking a question which cannot be explained using A Level knowledge.

However much of your answer was wrong, even in an A Level context.
My understanding of the difference between alicyclic and aromatic is perfectly adequate considering I got good marks on that particular topic at a-level. They explain to us the difference at A2 level without having to go into university level detail just fine
0
reply
alow
Badges: 19
Rep:
?
#12
Report 4 years ago
#12
They can't tell you the difference without aromatic and aliphatic without actually saying what an aromatic compound is. Therefore you don't know the difference.
0
reply
username1539513
Badges: 21
Rep:
?
#13
Report 4 years ago
#13
(Original post by alow)
They can't tell you the difference without aromatic and aliphatic without actually saying what an aromatic compound is. Therefore you don't know the difference.
They do talk about delocalised electrons though, which tends to distinguish an aromatic compound from an aliphatic compound (at least at a-level standard) I know that at university it's different because topics tend to get dumbed down at a-level
0
reply
alow
Badges: 19
Rep:
?
#14
Report 4 years ago
#14
Aliphatic compounds can have delocalised electrons too. That's not what makes an aromatic compound.

When I did A levels, my teacher taught us the proper characteristics of aromatics so it's hardly like "oh but it's at university" means an A level student can't appreciate and understand the complex.
0
reply
username1539513
Badges: 21
Rep:
?
#15
Report 4 years ago
#15
(Original post by alow)
Aliphatic compounds can have delocalised electrons too. That's not what makes an aromatic compound.

When I did A levels, my teacher taught us the proper characteristics of aromatics so it's hardly like "oh but it's at university" means an A level student can't appreciate and understand the complex.
That's true, but not all the way around the compound thus conferring it greater stability

That's kind of cool and I agree with you that just because someone is an a-level student they can't appreciate university concepts but they still have grades to get and irrelevant information could confuse them. You have to answer questions at a-level how the exam board wants you too in order to get that A or A*
0
reply
InadequateJusticex
Badges: 18
Rep:
?
#16
Report 4 years ago
#16
Erm...actually, conjugated compounds are not aromatic yet are definitely more stable than a molecule without conjugation or an alicylic compound due to their delocalised electrons (which don't actually extend to the whole molecule). So you're wrong.

Please don't argue about things you clearly have no clue about.
0
reply
InadequateJusticex
Badges: 18
Rep:
?
#17
Report 4 years ago
#17
(Original post by alow)
They can't tell you the difference without aromatic and aliphatic without actually saying what an aromatic compound is. Therefore you don't know the difference.
Savage.
1
reply
medhelp
Badges: 14
Rep:
?
#18
Report Thread starter 4 years ago
#18
alow guys you're confusing me sm lol
0
reply
InadequateJusticex
Badges: 18
Rep:
?
#19
Report 4 years ago
#19
(Original post by medhelp)
alow AngryRedhead guys you're confusing me sm lol
To put it simply, answer these two questions:

Is it a cyclic compound?
Is it aromatic? Refer to Huckel's rule above to correctly identify aromatic structures

If the answer to both questions is yes, then it's aromatic, not alicyclic. If the answer to 1 is yes and the answer to 2 is no, then it's alicyclic.
1
reply
username1539513
Badges: 21
Rep:
?
#20
Report 4 years ago
#20
(Original post by InadequateJusticex)
Erm...actually, conjugated compounds are not aromatic yet are definitely more stable than a molecule without conjugation or an alicylic compound due to their delocalised electrons (which don't actually extend to the whole molecule). So you're wrong.

Please don't argue about things you clearly have no clue about.
The OP specifically mentioned benzene so that is what my answer was based on. Even the OP has now said they are confused :rofl:
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (644)
33.45%
Yes, I like the idea of applying to uni after I received my grades (PQA) (816)
42.39%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (378)
19.64%
I think there is a better option than the ones suggested (let us know in the thread!) (87)
4.52%

Watched Threads

View All