DAT Question of the Day

Correct Answer: A. acetylene

Bond length is the distance between the centers of two covalently bonded atoms and is mostly dependent on atomic size, bond order (length: single > double > triple), and hybridization (C–H and C–C bonds shorten slightly with increased s character on carbon).

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Correct Answer: B. 10

Recall that the degrees of unsaturation corresponds to the sum of pi bonds and/or rings present in a molecule. Each ring and each pi bond contributes one degree of unsaturation; triple bonds, possessing one sigma and two pi bonds, contribute two degrees of unsaturation. Gestrinone has four rings (4), three alkenes (3), one carbonyl (1) and one alkyne (2). Thus IHD = 4 + 3 + 1 + 2 = 10

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Correct Answer: E. 1,4-dimethylcyclopent-1-ene

The treatment of alkenes with acidic potassium permanganate under high temperatures results in oxidative cleavage. The nature of the products are dependent on alkene substitution, but all with possess a carbonyl functionality (carboxylic acid, ketone, CO2). Looking at the product, one can identify the two carbon atoms of the original alkenyl compound, and work back accordingly. Finally, standard IUPAC naming will apply.

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Correct Answer: D. I and III

Aromatic compounds follow four rules: (1) They are conjugated—there needs to one “p” orbital from each atom in the ring, so each atom must be either sp² or sp hybridized; 2) They are cyclic: linear systems are not aromatic; 3) They are planar: there is good overlap/interaction between p orbitals; 4) they follow the The Huckel Rule—4n+2 π electrons in the cyclic conjugated π system (n = 0, 1, 2, 3 etc.). Of the possibilities,compounds I (14 e⁻, n = 3) and III (10 e⁻, n = 2) obey the rule.

This is a little advanced and at the top of the difficulty the DAT can throw at you, you have to consider compound 3 as one molecule, not two separate rings. Aromaticity requires a planar conjugated system, so we can ignore the bridge carbon sticking out of the plane of the rest of the molecule. There cannot be any sp3 atoms IN the aromatic ring. The carbon bridge actually pushes the 10 carbon ring to be planar, without it the molecule wouldn’t be aromatic.

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Correct Answer: D. The polarity of a molecule is dependent on its 3-D structure

A molecule’s dipole is an electric dipole with an inherent electric field (not be confused with a magnetic dipole which generates a magnetic field). Molecules can have dipole moments due to non-uniform distributions of positive and negative charges on the various atoms. For diatomic molecules there is only one (single or multiple) bond so the bond dipole moment is the molecular dipole moment, with typical values in the range of 0 to 11 D. For polyatomic molecules there is more than one bond, and the total molecular dipole moment may be approximated as the vector sum of all individual bond dipole moments.

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