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    I don't understand part of the mechanism when an amide attacks a halogenoalkane.

    Here's what I've written:

    Primary/secondary amines can act as nucleophiles (molecule/negatively charged ion containing a lone pair of electrons which it can donate to a positively charged ion to form a dative covalent bond) to react with halogenoalkanes to form secondary/tertiary amines. The carbon atom attached to the halogen will have a partial positive charge as halogens are very electronegative. The nucleophile attacks this carbon, forming a dative covalent bond from the nitrogen to the carbon. The bond between the carbon and the halogen breaks. The nitrogen atom now carries a positive charge. A bond between the nitrogen and hydrogen breaks, forming a secondary amine and hydrogen chloride. This is an alkylation reaction (hydrogen atoms are replaced by alkyl groups).

    The underlined part is the bit I don't understand. Why does the bond break? etc..

    Thank you
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    The hydrogen proton leaves the ammonium (N+) because the bonding electrons are drawn back to the electronegative nitrogen. This is more the more stable state, especially with a (mechanistically speaking) molar equivalent of chlorine ion by-products from the halogenoalkane around to accept protons.
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    The nitrogen is charged (high energy -> bad) it loses H+ to make itself more stable :yes:

    Not al halogens are 'very electronegative' by the way :p:
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    (Original post by EierVonSatan)
    The nitrogen is charged (high energy -> bad) it loses H+ to make itself more stable :yes:

    Not al halogens are 'very electronegative' by the way :p:
    Lol, okay thanks the halogens at the top are right

    And so... it's nothing to do with other nucleophiles reacting with it or anything? How does it lose it? Can you go in to a bit more detail?

    After the H+ has been lost does it react with the Cl- lost previously?
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    (Original post by SmileyGurl13)
    Lol, okay thanks the halogens at the top are right
    F and Cl are, but Br and I are not so electronegative :p: Nucleophilic substitution is faster with the latter two...but this is an aside :laugh:

    And so... it's nothing to do with other nucleophiles reacting with it or anything? How does it lose it? Can you go in to a bit more detail?

    After the H+ has been lost does it react with the Cl- lost previously?
    You'll see it drawn either as just the proton falling off or a base coming along to strip it off. In reality H+ doesn't exist on it's own and so something is stripping it off - that could be another amine or it might be a solvent molecule (depending on the solvent).

    HCl is a strong acid and (in aqueous media) will be completely dissociated into H+ and Cl- (which a very, very weak base). You could write the overall equation for a reaction (for example) like:

    RNH2 + CH3I ---> RNHCH3 + HI

    ...and that would be fine :yes:
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    (Original post by EierVonSatan)
    F and Cl are, but Br and I are not so electronegative :p: Nucleophilic substitution is faster with the latter two...but this is an aside :laugh:



    You'll see it drawn either as just the proton falling off or a base coming along to strip it off. In reality H+ doesn't exist on it's own and so something is stripping it off - that could be another amine or it might be a solvent molecule (depending on the solvent).

    HCl is a strong acid and (in aqueous media) will be completely dissociated into H+ and Cl- (which a very, very weak base). You could write the overall equation for a reaction (for example) like:

    RNH2 + CH3I ---> RNHCH3 + HI

    ...and that would be fine :yes:
    Hmm.. okay but how does an amine strip it off? :P I like to know it fully before I can understand it. xD weird, I know. Thank you very much, I will rep shortly.
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    (Original post by SmileyGurl13)
    Hmm.. okay but how does an amine strip it off? :P I like to know it fully before I can understand it. xD weird, I know. Thank you very much, I will rep shortly.
    The ammonium species is acidic: RNH3+

    A species acting as a base will remove the H+ from it, that could be another amine molecule, it could be solvent (such as water) it could be the iodide - it's not that relevant so long as you have something removing it but as I said above it can be drawn as it just 'falling off'.

    An explicit example:

    Spoiler:
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    (Original post by EierVonSatan)
    The ammonium species is acidic: RNH3+

    A species acting as a base will remove the H+ from it, that could be another amine molecule, it could be solvent (such as water) it could be the iodide - it's not that relevant so long as you have something removing it but as I said above it can be drawn as it just 'falling off'.

    An explicit example:

    Spoiler:
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    Your curly arrows aren't very curly EVS...

    ... is this a sign of impending old age?
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    (Original post by charco)
    Your curly arrows aren't very curly EVS...

    ... is this a sign of impending old age?
    Oi :p:

    Quite possibly! It's actually quite hard to find decent mechanism drawings on the net
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    (Original post by EierVonSatan)
    Oi :p:

    Quite possibly! It's actually quite hard to find decent mechanism drawings on the net
    Can I ask another quick chemistry question: why does heating cause the intermolecular bonds in a molecule to weaken?
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    (Original post by SmileyGurl13)
    Can I ask another quick chemistry question: why does heating cause the intermolecular bonds in a molecule to weaken?
    It's just like bonds within a molecule, if you put in energy you weaken and break them
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    (Original post by SmileyGurl13)
    Can I ask another quick chemistry question: why does heating cause the intermolecular bonds in a molecule to weaken?
    But... Why?
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    (Original post by SmileyGurl13)
    But... Why?
    If you want to consider it in more depth consider that the two particles bonded together are balls on a spring ...

    Heat does not weaken bonds 'per se'. The bond strength is a function of the nature of the particles that are held together, electron density etc etc.

    BUT

    All particles are in motion, and vibration is important in bonds. We also know that the force of attraction between two bonded particles is a function of the distance between them.

    Heat provides more vibrational energy, which makes the bonds need less 'extra energy' on average to break.

    So it is reasonable to say that a substance at higher temperature has weaker bonds. The particles bonded together are stretching (on average) further apart than at lower temperatures and need less of an extra push (read 'energy') to break the bond.
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    (Original post by EierVonSatan)
    It's just like bonds within a molecule, if you put in energy you weaken and break them
    But... Why?
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    Charco has given you an excellent explanation. You will never ever be asked in an exam to explain in that much depth!
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    (Original post by charco)
    If you want to consider it in more depth consider that the two particles bonded together are balls on a spring ...

    Heat does not weaken bonds 'per se'. The bond strength is a function of the nature of the particles that are held together, electron density etc etc.

    BUT

    All particles are in motion, and vibration is important in bonds. We also know that the force of attraction between two bonded particles is a function of the distance between them.

    Heat provides more vibrational energy, which makes the bonds need less 'extra energy' on average to break.

    So it is reasonable to say that a substance at higher temperature has weaker bonds. The particles bonded together are stretching (on average) further apart than at lower temperatures and need less of an extra push (read 'energy') to break the bond.
    To clarify say '.' are atoms in a bond like ._., normally they are like that but with heat they are vibrating more so at anyone point it might be like .__. so they are further apart and the bond is easier to break?
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    (Original post by SmileyGurl13)
    To clarify say '.' are atoms in a bond like ._., normally they are like that but with heat they are vibrating more so at anyone point it might be like .__. so they are further apart and the bond is easier to break?
    basically, yes
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    (Original post by charco)
    basically, yes
    Cheers m'dears
 
 
 
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