Turn on thread page Beta
    • Thread Starter
    Offline

    16
    ReputationRep:
    I understand that primary and secondary amines are stronger bases than aromatics.

    but is phenylmethylamine stronger than ammonia? and why?
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    22
    ReputationRep:
    The alkyl group is electron released. The lone pair on N is too far away from the delocalised electron system in Benzene.
    Ammonia has no alkyl groups in comparison.
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    14
    ReputationRep:
    Phenylmethylamine would behave like a primary amine so it would be stronger than ammonia due to the positive inductive effect. The methyl group would donate electron density to the nitrogen making the lone pair on nitrogen more diffuse thus increasing basicity by facilitating donation of electrons.
    Offline

    11
    ReputationRep:
    I think phenylmethylamine is weaker than ammonia because it’s a primary aromatic amine.

    Yes you’re right in saying primary and secondary amines are stronger than aromatics however the phenyl tells us that a benzene ring is attached to the NH2 and methyl group. The lone pair is less available due to the benzene ring drawing the electrons from the nitrogen atom towards itself therefore electron density on the nitrogen is lowered and the nitrogen’s lone pair is partially delocalised onto the ring.

    I hope this helps (Do let me know if I’ve gone wrong anywhere)
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    16
    ReputationRep:
    @ljcrisp
    @DrXavier

    ahh I'm confused, two contradicting points.
    is phenylmethylamine weaker or stronger?? 😕
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    14
    ReputationRep:
    Oh god I somehow misread the title as 'best of animes' and was seriously confused by the content here. Pretty ashamed tbh 😂
    Offline

    11
    ReputationRep:
    (Original post by Lia22)
    @ljcrisp
    @DrXavier

    ahh I'm confused, two contradicting points.
    is phenylmethylamine weaker or stronger?? 😕
    DrXavier without being rude at all, even though you’re right in saying primary amines are stronger bases than aromatics, the phenyl bit in phenylmethylamine indicates that there’s a benzene involved therefore phenylmethylamine is an aromatic.

    Lia22 This diagram may help
    Reference: CGP AQA A Level Chemistry: Year 2
    Name:  9708BC48-5378-42F9-978B-6B0CE81CAC41.jpg.jpeg
Views: 39
Size:  43.9 KB
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    11
    ReputationRep:
    (Original post by J...H)
    Oh god I somehow misread the title as 'best of animes' and was seriously confused by the content here. Pretty ashamed tbh 😂
    Don’t be ashamed 😂😂
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    21
    ReputationRep:
    Oh crap I saw the word anime...
    Offline

    20
    ReputationRep:
    I've got an amine burn scar on my leg.
    Offline

    14
    ReputationRep:
    (Original post by ljcrisp)
    DrXavier without being rude at all, even though you’re right in saying primary amines are stronger bases than aromatics, the phenyl bit in phenylmethylamine indicates that there’s a benzene involved therefore phenylmethylamine is an aromatic.

    Lia22 This diagram may help
    Reference: CGP AQA A Level Chemistry: Year 2
    Name:  9708BC48-5378-42F9-978B-6B0CE81CAC41.jpg.jpeg
Views: 39
Size:  43.9 KB
    I am afraid you are mistaken. If the phenyl was alpha to the nitrogen this would be correct, since it is beta, the aromatic group no longer withdraws electron density from the nitrogen.

    Without being rude, I am quite certain about the argument made (I tutor chemistry and one of my students got into Oxford for next year).

    In fact I just went and checked their respective pKb values phenylmethylamine has a pKb of 4.66 and ammonia a pKb of 4.75 which again tells you the phenylmethylamine is marginally a stronger base.
    Offline

    11
    ReputationRep:
    (Original post by DrXavier)
    I am afraid you are mistaken. If the phenyl was alpha to the nitrogen this would be correct, since it is beta, the aromatic group no longer withdraws electron density from the nitrogen.

    Without being rude, I am quite certain about the argument made (I tutor chemistry and one of my students got into Oxford for next year).

    In fact I just went and checked their respective pKb values phenylmethylamine has a pKb of 4.66 and ammonia a pKb of 4.75 which again tells you the phenylmethylamine is marginally a stronger base.
    Okay then if you say so I only meant if you’re looking from it as an A Level perspective. We’ve not learnt about pKb values for our specification but that’s good to know (I’m guessing then what it says in the book is another lie then?) Thank you!
    Posted on the TSR App. Download from Apple or Google Play
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by ljcrisp)
    Okay then if you say so I only meant if you’re looking from it as an A Level perspective. We’ve not learnt about pKb values for our specification but that’s good to know (I’m guessing then what it says in the book is another lie then?) Thank you!
    These concepts ARE an A level perspective.

    The "availabiity" of the lone pair to attract protons determines the base strength.

    This in turn depends induction and withdrawal, as outlined above.
    Offline

    14
    ReputationRep:
    (Original post by ljcrisp)
    Okay then if you say so I only meant if you’re looking from it as an A Level perspective. We’ve not learnt about pKb values for our specification but that’s good to know (I’m guessing then what it says in the book is another lie then?) Thank you!
    it isn't wrong - it applies to phenylamine (1) in the diagram I have drawn) but not phenylmethylamine (2) in the diagram I have drawn

    Name:  IMG_0128.jpg
Views: 43
Size:  266.2 KB

    you can see how in the first case the lone pair becomes less available so you can't donate it as well (thus less basic)

    in the second (this is phenylmethylamine) the phenyl group cannot do this but the methyl group can act as a donating group (hyperconjugation and all that jazz)
    Offline

    11
    ReputationRep:
    (Original post by charco)
    These concepts ARE an A level perspective.

    The "availabiity" of the lone pair to attract protons determines the base strength.

    This in turn depends induction and withdrawal, as outlined above.
    Yeah I agree with you on that. I just didn’t understand the alpha and beta that DrXavier was on about in terms of the nitrogen cause I’ve not been taught that for my A Level spec.
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    11
    ReputationRep:
    (Original post by DrXavier)
    it isn't wrong - it applies to phenylamine (1) in the diagram I have drawn) but not phenylmethylamine (2) in the diagram I have drawn

    Name:  IMG_0128.jpg
Views: 43
Size:  266.2 KB

    you can see how in the first case the lone pair becomes less available so you can't donate it as well (thus less basic)

    in the second (this is phenylmethylamine) the phenyl group cannot do this but the methyl group can act as a donating group (hyperconjugation and all that jazz)

    That makes sense! Thank you!!
    Posted on the TSR App. Download from Apple or Google Play
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by ljcrisp)
    Yeah I agree with you on that. I just didn’t understand the alpha and beta that DrXavier was on about in terms of the nitrogen cause I’ve not been taught that for my A Level spec.
    Alpha and beta are just old terminology used to refer to the relative positions of carbon atoms and their substituents.

    A carbon "next door" is referred to as an alpha carbon atom, and the next one along the chain is referred to as a beta carbon and so on through the Greek alphabet.

    It allows you to discuss carbon atoms that are near functional groups without having to use absolute numbering.

    For example CH3CH2CH2COCH2CH2CH3

    The alpha carbons are next to the carbonyl group. The hydrogen atoms on these carbons are also referred to as alpha hydrogens.

    If the chain is long. eg fatty acids, they may refer to the last carbon as the omega carbon and count using conventional number back from this one.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 4, 2018
The home of Results and Clearing

4,170

people online now

1,567,000

students helped last year

University open days

  1. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  2. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
  3. Bishop Grosseteste University
    All Courses Undergraduate
    Fri, 17 Aug '18
Poll
Will you be tempted to trade up and get out of your firm offer on results day?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.