Fact Questions

1.* (1996 F 10) Illustrate examples of each using structural formulas.

A. An antiaromatic hydrocarbon.

This must be a ring with alternating double bonds and a multiple of 4 electrons.

B. The smallest chiral hydrocarbon which shows every hybridization state of carbon.

 

C. Two molecules which are different but are composed of the same element, and no other atoms.

O2 and O3 (diamond and graphite aren't molecules)

Technically, 37Cl35Cl is different from 35Cl35Cl, and singlet O2 is different from triplet O2.

D. A prochiral olefin with 5 sites of unsaturation.

A prochiral olefin is not chiral but it reacts with chiral catalysts to form chiral products. While it will have symmetry in the double-bond sp2 plane, it can't have other symmetries.

 

E. The most powerful oxidizing agent in chemistry.

F2.

There are some other highly unstable oxidizing agents such as Pu+94, but you can't order them from a catalog or store them in a stockroom.

2.* (1996 F 14) Short Questions (warning: some of these are trickier than you first might think!)

A. Which has the shorter wavelength–infrared radiation or ultraviolet radiation?

UV has higher energy, higher frequency, and shorter wavelength than IR.

B. Which of the following separation technologies use an external electric field to cause the separation: solvent extraction, mass spectrometry, liquid chromatography, electrophoresis, centrifugation.

Mass spectrometry and electrophoresis depend on an external electric field.

  1. Name the symmetry elements that methane possesses.

Methane has E, C3, s, C2, and S4.

D. Circle those compounds that are optically active. H2C=C=CH2, H2C=C=CCl2, HClC=C=CBrH, HClC=C=CClH.

There are two optically active compounds. They are HClC=C=CBrH and HClC=C=CClH.

3.* (1995 F 2)

A. Describe one use of catalysts for improving the environment.

Automobile catalytic converters oxidize CO and unburned hydrocarbons.

B. Describe a catalytic reaction which degrades the environment.

Chlorine radicals catalyze ozone destruction in the upper atmosphere.

C. Give an example of a neutral molecule that is intrinsically unstable but can still be purchased.

H2O2, TNT, etc.

D. Give examples of two "allotropes" of the same element, one being diamagnetic and the other paramagnetic.

O2: paramagnetic

O3: diamagnetic

E. Give an example of a ligand which has neither electrons nor non-bonded electron pairs.

H, CH3, H2

F. Give an example of a metal complex with an anionic aromatic ligand, show the structure, indicate the oxidation state of the metal and the d-electron count.

 

G. Give two examples of oxidizing agents more powerful than molecular oxygen.

H2O2, O3, F2, singlet O2, etc.

H. Draw a stereochemical structure for a coordination complex which is chiral and has three unpaired electrons.

Cr(III) is d3, with 3 unpaired electrons

 

I. Identify the 4d metal in the following diamagnetic complex: M(CO)6. Give its d-electron configuration.

Mo(0) is d6.

CN- binds irreversibly to hemoglobin and myoglobin, preventing O2 from binding to them and thus destroying their catalytic properties (bringing oxygen to the body.) CO also blocks the binding of O2 to hemoglobin and myoglobin, but not as strongly.

4.* (1994 F 3) Give one example of each of the following; illustrate your answer by providing a structural formula:

A. Any naturally occurring a-amino acid. (show the exact stereochemistry).

glycine: R = H

alanine: R = -CH3

…and many more

B. An anti-aromatic compound containing only carbon and hydrogen.

1,3-cyclobutadiene

note: only thing preventing aromaticity is wrong number of -electrons

C. A transition metal cation having 5 unpaired electrons.

Fe(H2O)63+ high-spin d5 system complex has pos. charge (CATION)

D. A diamagnetic allotrope of oxygen.

O3 (ozone!)

E. A molecule having only sp hybridized atoms of two different kinds.

: N _ C -- C _ N : (cyanogen)

 

F. Any useful elastomer.

polyisoprene (natural rubber) once VULCANIZED… (cross-linked!)

4.* (1993 F 2) Using molecular formulas, llustrate specific examples of each of the following.

A. A diamagnetic, neutral molecule isolelectronic with the nitrite anion, NO2-

O3 (ozone)

 

 

B. Any "anti-aromatic" molecule.

An anti-aromatic molecule has conjugated double bonds in a ring. The number of -electrons is 4n, where n is an integer.

 

C. Any elastomer.

 

D. Any synthetic fiber used as a commercial product.

E. A very reactive gaseous molecule, produced as an intermediate in chemical manufacturing but not occuring in nature.

F2

F. A salt which contains no carbon but is used as a cheap high explosive (often when mixed with heating oil).

NH4NO3

G. A complex cation with 3 unpaired electrons, a charge of 3+, and chirality at the metal center.

 

Cr3+, d3

 

H. A hydrocarbon without chiral centers which exists as a mixture of enantiomers.

 

 

I. A gaseous diatomic molecule with 1 unpaired electron. This molecule is produced in the body and acts like a hormone.

NO

 

5.* (1990 F 2) Give an example of each of the following:

A. A reaction with negative enthalpy change and a positive entropy change:

Some examples:

B. A pure chemical substance characterized in the last two years:

C60 Buckminsterfullerene

C. A reaction which can be carried out directly or electrochemically:

 

D. An aromatic compound which contains no carbon:

 

E. A hydrocarbon which is chiral but has no chiral centers:

2,3-pentadiene (Another example is hexahelicene)