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    8. Substitution reactions at a saturated carbon atom are typified by the reaction of halogeno-alkanes with aqueous base to produce alcohols. Monumental work has been done and revealed two types of kinetic behaviour. These types are designated SN1 and SN2.
    (a) Outline the key differences between these two reaction mechanisms in terms of:
    (i) the structure of the starting halogeno-alkanes

    (ii) reaction intermediates and transition states

    (iii) Reaction mechanisms and the rate equations

    for this question , are my correct/

    i) primary haloalkanes go via SN2, tertiary haloalkanes go via SN1. Secondary ones go via a bit of both

    ii) in SN1 the reaction proceeds via a carbocation formed by the dissociation of the haloalkane.

    in SN2 the reaction proceeds via a transtition state formed by the temporary combination of the haloalkane and the attacking nucleophile

    are these two parts correct so far?
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    (Original post by otrivine)
    8. Substitution reactions at a saturated carbon atom are typified by the reaction of halogeno-alkanes with aqueous base to produce alcohols. Monumental work has been done and revealed two types of kinetic behaviour. These types are designated SN1 and SN2.
    (a) Outline the key differences between these two reaction mechanisms in terms of:
    (i) the structure of the starting halogeno-alkanes

    (ii) reaction intermediates and transition states

    (iii) Reaction mechanisms and the rate equations

    for this question , are my correct/

    i) primary haloalkanes go via SN2, tertiary haloalkanes go via SN1. Secondary ones go via a bit of both

    ii) in SN1 the reaction proceeds via a carbocation formed by the dissociation of the haloalkane.

    in SN2 the reaction proceeds via a transtition state formed by the temporary combination of the haloalkane and the attacking nucleophile

    are these two parts correct so far?
    Here's a video I prepared for just this topic:

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    (Original post by charco)
    Here's a video I prepared for just this topic:

    but is my answer wrong? is it worth 2 marks each
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    is my answer wrong for parts i) and ii)
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    (Original post by otrivine)
    is my answer wrong for parts i) and ii)
    The answer is in the video ...
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    (Original post by charco)
    The answer is in the video ...
    I appreciate it, but is my answer correct, cause I need to know if its wrong or right so I know my mistake,please Charco

    i) primary haloalkanes go via SN2, tertiary haloalkanes go via SN1. Secondary ones go via a bit of both

    ii) in SN1 the reaction proceeds via a carbocation formed by the dissociation of the haloalkane.

    in SN2 the reaction proceeds via a transtition state formed by the temporary combination of the haloalkane and the attacking nucleophile
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    (Original post by otrivine)
    I appreciate it, but is my answer correct, cause I need to know if its wrong or right so I know my mistake,please Charco

    i) primary haloalkanes go via SN2, tertiary haloalkanes go via SN1. Secondary ones go via a bit of both

    ii) in SN1 the reaction proceeds via a carbocation formed by the dissociation of the haloalkane.

    in SN2 the reaction proceeds via a transtition state formed by the temporary combination of the haloalkane and the attacking nucleophile
    The answers to these questions are stated quite clearly in the video ...
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    (Original post by charco)
    The answers to these questions are stated quite clearly in the video ...
    ok will look , and this question
    (b) When one optical isomer of 2-bromobutane undergoes a nucleophilic substitution reaction with aqueous base, the product is a racemic mixture of the corresponding tertiary alcohol. Explain how this comes about with reference to the appropriate reaction mechanism.

    I got
    The fact that the product is racemic (ie a mixture of both R and S enantiomers) tells you the reaction muct have gone via SN1, rather than SN2.

    In an SN2 reaction, the nucleophile attacks from the opposite side to the leaving group. This means that the stereochemistry is inverted (ie an R starting material becomes an S product, and vice versa).

    But in an SN1 reaction, the reaction proceeds via a carbocation, which is planar. Therefore the original stereochemistry of the starting material is lost and the nucleophille can attack from either side. This leads to an equal mix of R and S enantiomers in the product (what we call a racemic mixture).
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    (Original post by otrivine)
    ok will look , and this question
    (b) When one optical isomer of 2-bromobutane undergoes a nucleophilic substitution reaction with aqueous base, the product is a racemic mixture of the corresponding tertiary alcohol. Explain how this comes about with reference to the appropriate reaction mechanism.

    I got
    The fact that the product is racemic (ie a mixture of both R and S enantiomers) tells you the reaction muct have gone via SN1, rather than SN2.

    In an SN2 reaction, the nucleophile attacks from the opposite side to the leaving group. This means that the stereochemistry is inverted (ie an R starting material becomes an S product, and vice versa).

    But in an SN1 reaction, the reaction proceeds via a carbocation, which is planar. Therefore the original stereochemistry of the starting material is lost and the nucleophille can attack from either side. This leads to an equal mix of R and S enantiomers in the product (what we call a racemic mixture).
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    (Original post by charco)
    and should I include diagrams?
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    (Original post by otrivine)
    and should I include diagrams?
    A picture is worth a thousand words. True as much in chemistry as anything else.
 
 
 
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