Title: Carbonyl chemistry 2009 Quiz 1

Feedback shared by this category's questions, if partly right: 1

Q: The inductive effect is a long range effect that operates over many atoms.
- true
- false
A: false

Q: Which of the following molecules has a dipole moment, CH_4, CH_3Cl, CH_2Cl_2, CH_3Cl, CCl_4?
- CH_4, CH_3Cl, CH_2Cl_2, CH_3Cl, CCl_4
- CH_3Cl, CH_2Cl_2, CH_3Cl, CCl_4
- CH_3Cl, CH_2Cl_2, CH_3Cl
- CH_3Cl, CH_3Cl, CCl_4
A: CH_3Cl, CH_2Cl_2, CH_3Cl

Q: Linus Pauling was a remarkable scientist who made important contributions to several areas of science. In 1954 he received the Nobel Prize in Chemistry for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances. In what field did Pauling win his second Nobel Prize in 1962?
- Medicine
- Physics
- Peace
- Chemistry
A: Peace

Q: In the molecule pyridine the nitrogen atom (Z=7) is sp^2 hybridised. This means that the 2s and 2p orbitals are hybridised to give an electron configuration where there are? [Image: pyridine]
- Two sp^2 hybrid orbitals each containing one electron and one sp^2 hybrid orbital containing two electrons and one unhybridised sp orbital containing one electron
- Two sp^2 hybrid orbitals each containing two electron and one sp^2 hybrid orbital containing one electron
- Three sp^2 hybrid orbitals each containing one electron and one unhybridised sp orbital containing two electrons
- Two sp^2 hybrid orbitals each containing one electron and one unhybridised sp orbital containing one electron
A: Two sp^2 hybrid orbitals each containing one electron and one sp^2 hybrid orbital containing two electrons and one unhybridised sp orbital containing one electron

Q: A molecule is polar and has a DIPOLE MOMENT if "the centre of mass of all positive charges and the centre of mass of all negative charges are not coincidental
- true
- false
A: true

Q: A Bronsted acid is a substance that donates a proton and a Lewis acid is a substance that accepts an electron pair.
- true
- false
A: true

Q: because of the lone pair of electrons an amine with three different substituents is chiral.
- true
- false
A: false

Q: Generally arylamines are more basic than alkylamines because the nitrogen lone-pair is delocalised by interactions with the aromatic ring pi-electron system.
- true
- false
A: false

Q: Carboxylic acids often have higher boiling points that corresponding alcohols e.g. ethanol b.p. 78 C, acetic acid b.p. 118 C and benzyl alcohol b.p. 205 C and benzoic acid b.p. 249 C. Why do carboxylic acids have higher boiling points?
- Carboxylic acids have an extra oxygen atom so they have higher molecular weights and higher boiling point.
- Carboxylic acids are dissociated in solution so they have much higher boiling points.
- Carboxylic acids are strongly associated because of hydrogen bonding.
- Carboxylic acids are usually solids and solids have higher boiling points than liquids.
A: Carboxylic acids are strongly associated because of hydrogen bonding.

Q: All of the following species are Lewis acids, BCl_3, AlBr_3 and H^+.
- true
- false
A: true

Q: In aqueous solution it is impossible to have an acid with a pK_a lower than -1.74. Why?
- Water is the solvent, so its concentration is approximately 55 M and it can be considered constant.
- Many acid molecules do not ionise fully in water.
- In water H_3O^+ is the strongest possible acid.
- Acids of the form HA are fully ionised giving H^+ and A^-
A: In water H_3O^+ is the strongest possible acid.

Q: Rank the following acidic compounds from strongest to weakest acid [Image: pkas]
- III, I, II, IV
- I, III, IV, II
- II, IV, III, I
- III, II, IV, I
A: I, III, IV, II

Q: Rank the following acidic molecules from strongest to weakest acid [Image: acidstrength02]
- III, I, IV, II
- I, III, II, IV
- IV, II, I, III
- II, IV, I, III
A: II, IV, I, III

Q: Given that F is more electronegative than Cl, why is BF_3 a weaker Lewis acid than BCl_3? (As judged by the relative enthalpy change on adduct formation)
- The steric effects of the Cl atoms result in a large negative enthalpy of formation.
- There is a larger degree of pi-bonding in BF_3 than BCl_3.
- HCl is a better proton donor and hence a stronger acid than HF.
- The electronegative F atoms make the boron atom very electropositive.
A: There is a larger degree of pi-bonding in BF_3 than BCl_3.

Q: in aqueous solution (CH_3)_3N is a weaker base than (CH_3)_2NH but in aportic solvents such as chlorobenzene this relationship is reversed. Why?
- Hydrogen bonding in water helps to stabilise the ammonium ion and (CH_3)_2NH can form more hydrogen bonds than (CH_3)_3N.
- The methyl groups are less electron releasing in water than chlorobenzene because of hydrogen bonding.
- In water (CH_3)_3N is partially protonated and thus acts as a weak acid.
- Because of the extra methyl group (CH_3)_3N is much more soluble than (CH_3)_2NH.
A: Hydrogen bonding in water helps to stabilise the ammonium ion and (CH_3)_2NH can form more hydrogen bonds than (CH_3)_3N.