18) (--Mandelic acid has - A)-6 Ha.innofaw what would beth.spelkiotason of a soh
ID: 544660 • Letter: 1
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18) (--Mandelic acid has - A)-6 Ha.innofaw what would beth.spelkiotason of a sohation mandel 8 +32 19) Which of the statements below corectly 19 deribes an achiral molecsle? acnvity A) The molecule exhilbits B) The mobdts optical ackivity when it Interact with plane-polarized Wg. molecule has an enantiomer C) The molecule might be a meso form The oecule has a nomsuperimposable márror imag E) none of the above 20) Which of the 20) following statements correctly pertains to a pair of enantiomers? have different melting points B) They rotate the plane of polarieed lighi by differing amounts and in the sanne direction. They rolate the plane ol poilaried lught by diltering amou ndinps dirertions D) They have the same melting point, but they have different boiling points he same amount and in opposite hey rotate the plane of polarized light by exactly t d directions 21. whioh of the following oyaloalkane has the lovest ring strain (E) eyoloheptane (C) eyolopen tane (D) ayalohexane (A) oyelopropane , "(A) 1 (B) ayolobutane 2. Musber of aikyi broaide soer vith forauia ca (C) 3 (D) 4 (R) S (B) 2 23. Number of asyanetria oarbons in 2-mothyloyelopentanol (R) 4 (C)2 (D) 3 (A) O (B) 1 24. R/s Labela of the following chiral compounda are: Ho (E) can not be deterained (A) R,R (B) S,S(C) R,S(D) S,R 25. Number of secondary carbons in the following compounds are: (E) 6, 3 (D) 8, 3 (C) 6, 2 (A) 6, 4(B) 8, 4Explanation / Answer
answer 18) optical activity is the ability to rotate plane polalized light
(-)-mandelic acid has optical rotation -158o
(+)-mandelic acid has optical activity +158o
so mixture of 40% (-) and 60% (+) will have optical rotation of +32o
optical rotation = [0.40*(-158o) + 0.60*(+158o) = +32o
answer 19)answer is c because
A molecule is achiral if it is superimposable on its mirror image. Most achiral molecules do have a plane of symmetry or a center of symmetry. Achiral molecules that contain a stereocenter are called meso.
answer 20) answer is E because
Enantiomers possess identical chemical structures but are mirror images of one another Therefore, their electron clouds are also identical but actually mirror images of one another and not superimposable. For this reason, enantiomeric pairs rotate light by the same magnitude (number of degrees), but they each rotate plane polarized light in opposite directions
answer 21) answer is D cyclohexane
in cycloalkane system only cyclohexane is the one which has minimum ring strain almost 0.4Kcal/mol
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