LDA and an aldehyde Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Selectivity in aldol condensation between pivaldehyde and acetoneWhy can you not make a compound with a quaternary alpha carbon using malonic ester?How to explain the different regioselectivity of ketones/imines reacting with LDA?nucleophilic attack in Acid chloride formationWhy is Fmoc base-labile and Moz acid-labile?Can a base like OH- attack aldehyde and ketone to create hydrate instead of enol?Can aldol reaction occur during α-halogenation of ketone?Synthesis of methylenecyclohexane from cyclohexylmethanolReduction of Carbonyl Compounds with LiAlH4Salt used in Perkin Reaction

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LDA and an aldehyde

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LDA and an aldehyde



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Selectivity in aldol condensation between pivaldehyde and acetoneWhy can you not make a compound with a quaternary alpha carbon using malonic ester?How to explain the different regioselectivity of ketones/imines reacting with LDA?nucleophilic attack in Acid chloride formationWhy is Fmoc base-labile and Moz acid-labile?Can a base like OH- attack aldehyde and ketone to create hydrate instead of enol?Can aldol reaction occur during α-halogenation of ketone?Synthesis of methylenecyclohexane from cyclohexylmethanolReduction of Carbonyl Compounds with LiAlH4Salt used in Perkin Reaction










3












$begingroup$



Compounds A and B both react with LDA (lithium diisopropylamide, a strong base) to form the same anion C with the formula $ceC4H5O^-Li^+$.



LDA reaction scheme




I am unfamiliar with LDA. My first thought was that the base would attack the H of the carbonyl C, I presumed that this H would have the lowest $mathrmpK_mathrma$ because it is an $mathrmsp^2$ C and the C is slightly positive from the carbonyl.



However, the structures this gave were confusing and didn't give the same product for both A and B. I tried to google LDA which showed that it was a big bulky base so it can't attack hindered H, but this shouldn't be a problem as the carbonyl C H isn't hindered. However, I found one mechanism for a different aldehyde that had the H taken from the $mathrmsp^3$ C next to the carbonyl.



Where would LDA preferentially attack an aldehyde and why?



Additional note: I have now played around with the structures to find that the only way LDA could react with A and B to form the same anion C if it in both cases it removes and $ceH+$ from the $mathrmsp^3$ carbon in the structure, these seems counter-intuitive! But perhaps LDA only attacks $mathrmsp^3$ C-H for some reason?










share|improve this question











$endgroup$











  • $begingroup$
    LDA is a very strong base and not fussy about whether it takes an alpha proton or a gamma proton because you will end up with the same extended enolate i.e. C, which is a stable species.
    $endgroup$
    – Waylander
    4 hours ago











  • $begingroup$
    While this question has a good goal, I think it is a terrible question, if this is a homework or exam question, or just an incomplete question if you're asking it yourself. Which enolate should be produced under the circumstances? (E)- or (Z)- ? They are different, non-interconverting, and probably formed in a mixture whose composition is dependent on whether you start from A or B.
    $endgroup$
    – Zhe
    2 hours ago
















3












$begingroup$



Compounds A and B both react with LDA (lithium diisopropylamide, a strong base) to form the same anion C with the formula $ceC4H5O^-Li^+$.



LDA reaction scheme




I am unfamiliar with LDA. My first thought was that the base would attack the H of the carbonyl C, I presumed that this H would have the lowest $mathrmpK_mathrma$ because it is an $mathrmsp^2$ C and the C is slightly positive from the carbonyl.



However, the structures this gave were confusing and didn't give the same product for both A and B. I tried to google LDA which showed that it was a big bulky base so it can't attack hindered H, but this shouldn't be a problem as the carbonyl C H isn't hindered. However, I found one mechanism for a different aldehyde that had the H taken from the $mathrmsp^3$ C next to the carbonyl.



Where would LDA preferentially attack an aldehyde and why?



Additional note: I have now played around with the structures to find that the only way LDA could react with A and B to form the same anion C if it in both cases it removes and $ceH+$ from the $mathrmsp^3$ carbon in the structure, these seems counter-intuitive! But perhaps LDA only attacks $mathrmsp^3$ C-H for some reason?










share|improve this question











$endgroup$











  • $begingroup$
    LDA is a very strong base and not fussy about whether it takes an alpha proton or a gamma proton because you will end up with the same extended enolate i.e. C, which is a stable species.
    $endgroup$
    – Waylander
    4 hours ago











  • $begingroup$
    While this question has a good goal, I think it is a terrible question, if this is a homework or exam question, or just an incomplete question if you're asking it yourself. Which enolate should be produced under the circumstances? (E)- or (Z)- ? They are different, non-interconverting, and probably formed in a mixture whose composition is dependent on whether you start from A or B.
    $endgroup$
    – Zhe
    2 hours ago














3












3








3





$begingroup$



Compounds A and B both react with LDA (lithium diisopropylamide, a strong base) to form the same anion C with the formula $ceC4H5O^-Li^+$.



LDA reaction scheme




I am unfamiliar with LDA. My first thought was that the base would attack the H of the carbonyl C, I presumed that this H would have the lowest $mathrmpK_mathrma$ because it is an $mathrmsp^2$ C and the C is slightly positive from the carbonyl.



However, the structures this gave were confusing and didn't give the same product for both A and B. I tried to google LDA which showed that it was a big bulky base so it can't attack hindered H, but this shouldn't be a problem as the carbonyl C H isn't hindered. However, I found one mechanism for a different aldehyde that had the H taken from the $mathrmsp^3$ C next to the carbonyl.



Where would LDA preferentially attack an aldehyde and why?



Additional note: I have now played around with the structures to find that the only way LDA could react with A and B to form the same anion C if it in both cases it removes and $ceH+$ from the $mathrmsp^3$ carbon in the structure, these seems counter-intuitive! But perhaps LDA only attacks $mathrmsp^3$ C-H for some reason?










share|improve this question











$endgroup$





Compounds A and B both react with LDA (lithium diisopropylamide, a strong base) to form the same anion C with the formula $ceC4H5O^-Li^+$.



LDA reaction scheme




I am unfamiliar with LDA. My first thought was that the base would attack the H of the carbonyl C, I presumed that this H would have the lowest $mathrmpK_mathrma$ because it is an $mathrmsp^2$ C and the C is slightly positive from the carbonyl.



However, the structures this gave were confusing and didn't give the same product for both A and B. I tried to google LDA which showed that it was a big bulky base so it can't attack hindered H, but this shouldn't be a problem as the carbonyl C H isn't hindered. However, I found one mechanism for a different aldehyde that had the H taken from the $mathrmsp^3$ C next to the carbonyl.



Where would LDA preferentially attack an aldehyde and why?



Additional note: I have now played around with the structures to find that the only way LDA could react with A and B to form the same anion C if it in both cases it removes and $ceH+$ from the $mathrmsp^3$ carbon in the structure, these seems counter-intuitive! But perhaps LDA only attacks $mathrmsp^3$ C-H for some reason?







organic-chemistry reaction-mechanism






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 40 mins ago









andselisk

19.6k665128




19.6k665128










asked 4 hours ago









MirteMirte

21919




21919











  • $begingroup$
    LDA is a very strong base and not fussy about whether it takes an alpha proton or a gamma proton because you will end up with the same extended enolate i.e. C, which is a stable species.
    $endgroup$
    – Waylander
    4 hours ago











  • $begingroup$
    While this question has a good goal, I think it is a terrible question, if this is a homework or exam question, or just an incomplete question if you're asking it yourself. Which enolate should be produced under the circumstances? (E)- or (Z)- ? They are different, non-interconverting, and probably formed in a mixture whose composition is dependent on whether you start from A or B.
    $endgroup$
    – Zhe
    2 hours ago

















  • $begingroup$
    LDA is a very strong base and not fussy about whether it takes an alpha proton or a gamma proton because you will end up with the same extended enolate i.e. C, which is a stable species.
    $endgroup$
    – Waylander
    4 hours ago











  • $begingroup$
    While this question has a good goal, I think it is a terrible question, if this is a homework or exam question, or just an incomplete question if you're asking it yourself. Which enolate should be produced under the circumstances? (E)- or (Z)- ? They are different, non-interconverting, and probably formed in a mixture whose composition is dependent on whether you start from A or B.
    $endgroup$
    – Zhe
    2 hours ago
















$begingroup$
LDA is a very strong base and not fussy about whether it takes an alpha proton or a gamma proton because you will end up with the same extended enolate i.e. C, which is a stable species.
$endgroup$
– Waylander
4 hours ago





$begingroup$
LDA is a very strong base and not fussy about whether it takes an alpha proton or a gamma proton because you will end up with the same extended enolate i.e. C, which is a stable species.
$endgroup$
– Waylander
4 hours ago













$begingroup$
While this question has a good goal, I think it is a terrible question, if this is a homework or exam question, or just an incomplete question if you're asking it yourself. Which enolate should be produced under the circumstances? (E)- or (Z)- ? They are different, non-interconverting, and probably formed in a mixture whose composition is dependent on whether you start from A or B.
$endgroup$
– Zhe
2 hours ago





$begingroup$
While this question has a good goal, I think it is a terrible question, if this is a homework or exam question, or just an incomplete question if you're asking it yourself. Which enolate should be produced under the circumstances? (E)- or (Z)- ? They are different, non-interconverting, and probably formed in a mixture whose composition is dependent on whether you start from A or B.
$endgroup$
– Zhe
2 hours ago











1 Answer
1






active

oldest

votes


















3












$begingroup$

If electronegativity alone were the only factor in determining the acidity of a carbon-hydrogen bond, the base would in fact attack the aldehyde hydrogen. But that is not so, for delocalization of negative charge can also stabilize the anion. If the base attacks at the initially saturated carbon in either compound, you get a delocalized negative charge distributed throughout the carbon chain and onto the oxygen.



Such delocalization stabilizes the anion so strongly that it overrides the original electronegativity difference between $mathrmsp^2$ and $mathrmsp^3$ carbon atoms. So, the base will attack along the carbon chain to produce this delocalized charge anion, instead of at the carbonyl carbon which offers no such delocalization.






share|improve this answer











$endgroup$













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    1 Answer
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    1 Answer
    1






    active

    oldest

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    active

    oldest

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    active

    oldest

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    3












    $begingroup$

    If electronegativity alone were the only factor in determining the acidity of a carbon-hydrogen bond, the base would in fact attack the aldehyde hydrogen. But that is not so, for delocalization of negative charge can also stabilize the anion. If the base attacks at the initially saturated carbon in either compound, you get a delocalized negative charge distributed throughout the carbon chain and onto the oxygen.



    Such delocalization stabilizes the anion so strongly that it overrides the original electronegativity difference between $mathrmsp^2$ and $mathrmsp^3$ carbon atoms. So, the base will attack along the carbon chain to produce this delocalized charge anion, instead of at the carbonyl carbon which offers no such delocalization.






    share|improve this answer











    $endgroup$

















      3












      $begingroup$

      If electronegativity alone were the only factor in determining the acidity of a carbon-hydrogen bond, the base would in fact attack the aldehyde hydrogen. But that is not so, for delocalization of negative charge can also stabilize the anion. If the base attacks at the initially saturated carbon in either compound, you get a delocalized negative charge distributed throughout the carbon chain and onto the oxygen.



      Such delocalization stabilizes the anion so strongly that it overrides the original electronegativity difference between $mathrmsp^2$ and $mathrmsp^3$ carbon atoms. So, the base will attack along the carbon chain to produce this delocalized charge anion, instead of at the carbonyl carbon which offers no such delocalization.






      share|improve this answer











      $endgroup$















        3












        3








        3





        $begingroup$

        If electronegativity alone were the only factor in determining the acidity of a carbon-hydrogen bond, the base would in fact attack the aldehyde hydrogen. But that is not so, for delocalization of negative charge can also stabilize the anion. If the base attacks at the initially saturated carbon in either compound, you get a delocalized negative charge distributed throughout the carbon chain and onto the oxygen.



        Such delocalization stabilizes the anion so strongly that it overrides the original electronegativity difference between $mathrmsp^2$ and $mathrmsp^3$ carbon atoms. So, the base will attack along the carbon chain to produce this delocalized charge anion, instead of at the carbonyl carbon which offers no such delocalization.






        share|improve this answer











        $endgroup$



        If electronegativity alone were the only factor in determining the acidity of a carbon-hydrogen bond, the base would in fact attack the aldehyde hydrogen. But that is not so, for delocalization of negative charge can also stabilize the anion. If the base attacks at the initially saturated carbon in either compound, you get a delocalized negative charge distributed throughout the carbon chain and onto the oxygen.



        Such delocalization stabilizes the anion so strongly that it overrides the original electronegativity difference between $mathrmsp^2$ and $mathrmsp^3$ carbon atoms. So, the base will attack along the carbon chain to produce this delocalized charge anion, instead of at the carbonyl carbon which offers no such delocalization.







        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited 39 mins ago









        andselisk

        19.6k665128




        19.6k665128










        answered 3 hours ago









        Oscar LanziOscar Lanzi

        16.3k12749




        16.3k12749



























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