Final answer:
The structure of a four-carbon alcohol with a molecular ion at m/z = 74 that also fragments at m/z = 59, 56, and 45 is butan-2-ol. The fragments are formed due to the loss of specific groups and the cleavage of C-C bonds. This molecule has tetrahedral geometry at each carbon atom.
Step-by-step explanation:
The structure of a four-carbon alcohol that exhibits a molecular ion at m/z = 74 and produces fragments at m/z = 59, m/z = 56, and m/z = 45 is butan-2-ol. The presence of these fragments suggests that the molecular structure has a central alcohol functional group.
The molecule can fragment in a mass spectrometer to yield these masses in several ways. The loss of a methyl group (CH3) can lead to a fragment at m/z = 59, which corresponds to the C3H7O+ ion. Loss of water (m/z = 18) from the molecular ion can result in a fragment at m/z = 56 (C4H8+). Finally, cleavage of the C-C bond next to the oxygen could yield a propyl cation (C3H7+) at m/z = 45.
The molecular geometry of butan-2-ol involves tetrahedral geometry at each carbon atom due to the four single bonds they form. The hydroxyl group adds polarity to the molecule, which influences the boiling and melting points.