Which molecule contains 2 potential stereocentres?

#a.# #"H"_3"CCH(OH)CH"_2"CH"_3#
#b.# #"H"_3"CCH(OH)CH(OH)CH"_3#
#c.# #"H"_3"CCClHCH"_3#
#d.# #"H"_3"CC(=O)Cl"#

In addition, is it TRUE that the molecular ion has essentially the same mass as its parent molecule.

1 Answer
anor277
Aug 17, 2017

Well, I would choose #"option b"#.

Explanation:

To a first approx. we can often identify a chiral carbon centre by the presence of FOUR different substituents. #b,# fits this criterion for the two adjacent carbons. #a.# and #c# possess only the one stereocentre. #d.# is achiral.

In mass spectrometry, the molecular ion has essentially the same mass as the parent molecule, and thus the given propostion is #"TRUE"#. Of course the keyword is #"essentially"#. The actual ion observed is likely the molecule LESS one electron, i.e. #M^+#. Since electrons have negligible mass, to a a first approx. #M# has the same mass as #M^+#.

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