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Punjab Medical Punjab - MET Solved Paper-2011

  • question_answer
    Which of the following is threo isomer? \[\underset{(I)}{\mathop{\underset{A}{\mathop{\underset{X-\underset{|}{\overset{|}{\mathop{C-}}}\,Z}{\overset{\begin{smallmatrix}  Y \\  | \end{smallmatrix}}{\mathop{X-C-Z}}}\,}}\,}}\,\,\,\,\,\,\,\,\underset{(II)}{\mathop{\underset{A}{\mathop{\underset{Z-\underset{|}{\overset{|}{\mathop{C-}}}\,X}{\overset{\begin{smallmatrix}  Y \\  | \end{smallmatrix}}{\mathop{X-C-Z}}}\,}}\,}}\,\,\,\,\,\,\,\,\underset{(III)}{\mathop{\underset{A}{\mathop{\underset{Z-\underset{|}{\overset{|}{\mathop{C-}}}\,X}{\overset{\begin{smallmatrix}  Y \\  | \end{smallmatrix}}{\mathop{X-C-Y}}}\,}}\,}}\,\]

    A)  Only I

    B)  Only II

    C)  Only III

    D)  All of the above

    Correct Answer: B

    Solution :

    Erythro and \[threo\] prefixes are used in systems containing two such asymmetric carbon atoms in which two substituents on each carbon are identical and third is different. Thus, in such cases, the isomer having identical groups on the same side is called erythro and that having identical groups on the opposite side is called\[threo\]. \[\underset{Threo}{\mathop{\underset{A}{\mathop{\underset{Z-\underset{|}{\overset{|}{\mathop{C-}}}\,X}{\overset{\begin{smallmatrix}  Y \\  | \end{smallmatrix}}{\mathop{X-C-Z}}}\,}}\,}}\,\,\,\,\,\,\,\,\underset{Erythro}{\mathop{\underset{A}{\mathop{\underset{X-\underset{|}{\overset{|}{\mathop{C-}}}\,Z}{\overset{\begin{smallmatrix}  Y \\  | \end{smallmatrix}}{\mathop{X-C-Z}}}\,}}\,}}\,\]


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