B555`S CHEMISTRY HUB

22]. What do you mean by 'Complete Delocalisation of Electrons', a neccesity for aromaticity by Huckel's rule? Is it possible to judge from the structure of a compound whether complete delocalisation of electrons is available or not?

23]Why is monobromination of aromatic ring observed when the ring is treated with Br2 in presense of CS2?

24]

33 Which of the following statements is true for a pair of diastereomers?
A) they will have identical physiological properties.
B) they will have specific rotations of opposite sign.
C) they will have identical chemical properties (e.g. reactivity)
D) they will have different physical properties.

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34 Which of the following descriptive terms would never be applied to a pair of stereoisomers ?
A) enantiomers
B) tautomers
C) diastereomers
D) epimers

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35 What kind of reagent would be needed to resolve a racemic amine, such as 2-aminobutane ?
A) the pure optically active amine to serve as a template for crystallization.
B) an achiral carboxylic acid to give a racemic mixture of amine salts.
C) an enantiomerically pure chiral carboxylic acid to give a diastereomeric mixture of amine salts.
D) a racemic chiral carboxylic acid to give a complete mixture of isomeric amine salts.

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36 What common symmetry elements if any are found in the stable chair conformer of trans-1,4-dichlorocyclohexane?
A) a single mirror plane and a C2 rotational axis.
B) a C3 rotational axis but no mirror plane.
C) two orthogonal mirror planes and a C2 rotational axis.
D) a single C2 rotational axis but no mirror plane.

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37 What common symmetry elements if any are found in the stable chair conformer of trans-1,2-dichlorocyclohexane?
A) a single mirror plane and a C2 rotational axis.
B) a single mirror plane and a C3 rotational axis.
C) two orthogonal mirror planes and a C2 rotational axis.
D) a single C2 rotational axis but no mirror plane.

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38 Reaction of 3-methyl-1,4-cycloheptadiene with excess perbenzoic acid (C6H5CO3H) forms a diepoxide product.
How many stereoisomers, counting enantiomers, are expected from this reaction ?
A) 4 (two pairs of enantiomers)
B) 4 (two meso compounds and a pair of enantiomers)
C) 5 (two pairs of enantiomers and a meso compound)
D) 6 (two pairs of enantiomers and two meso compounds)

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39 The antimalarial alkaloid quinine, C20H24N2O2, is optically active.
An ethanol solution of 8g quinine in 100mL displays a rotation of -13.6º in a 1dm polarimeter tube.
What is the specific rotation of quinine?
A) -85º
B) -170º
C) -43º
D) -26º

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41 Which of the following compounds has a prochiral methylene group (i.e. the hydrogen atoms are diastereotopic)?
A) propane , CH3CH2CH3
B) cyclopropane , (CH2)3
C) 2-methylpropene , CH2=C(CH3)2
D) ethanol , CH3CH2OH

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42 The thermal electrocyclic closure of (2E,4Z,6E)-2,4,6-octatriene gives which of the following?
A) cis-5,6-dimethyl-1,3-cyclohexadiene
B) trans-5,6-dimethyl-1,3-cyclohexadiene
C) cis-3,6-dimethyl-1,4-cyclohexadiene
D) cis-3,6-dimethyl-1,4-cyclohexadiene

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43 The Cope rearrangement, [3,3]-sigmatropic shift, of meso-3,4-dimethyl-1,5-hexadiene gives which of the following?
A) 1,7-octadiene
B) (2Z,6Z)-2,6-octadiene
C) (2E,6Z)-2,6-octadiene
D) (2E,6E)-2,6-octadiene

49 Which of the following statements is not an essential feature of an optically active compound?
A) the molecules of an optically active compound will be dissymetric or asymmetric.
B) the molecules of an optically active molecule must have at least one stereogenic site.
C) an optically active compound's molecular configuration will not be identical with its mirror image.
D) an optically active compound will have at least one stereoisomer.

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50 Which of the following statements is not correct?
A) a pair of enantiomeric compounds will have the same melting point.
B) a pair of enantiomeric compounds will have the same solubility in ethanol.
C) a pair of enantiomeric compounds will have exactly the same functional groups.
D) a pair of enantiomeric compounds will have identical optical rotations.

General and Miscelleneous
1. How many electrons occupy the bonding molecular orbitals of a CN triple bond?
A) 2 B) 4 C) 6 D) 8

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2. Which of the following species is not amphoteric ?
A) NH3 B) HF C) NH4(+) D) HCO3(-)

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3 What is the relationship of the two structures shown below?

A) they are identical.
B) they are conformations of the same structure
C) they are constitutional isomers.
D) they are different compounds with different compositions

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4 Which of the following molecules will not have a dipole moment?
A) CH3Cl
B) CH3OCH3
C) CH2Cl2
D) CCl4

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5 Which of the following molecules has a dipole moment?
A) CBr4
B) CH2=CH2
C) BF3
D) SO2

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6 Which of the following molecules has a linear shape?
A) NH3
B) H2S
C) CO2
D) H2CO

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7 Which of the following intermediates is pyramidal in shape?
A) H3C(+)
B) H2C:
C) H3C:(-)
D) HC≡C:(-)

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8 In which compound does carbon have the highest oxidation state?
A) CH4
B) HCN
C) H2CO
D) CH2Cl2

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9 Which of the following statements applies to a C10H14O2 compound?
A) it may have 2 double bonds and 2 rings
B) it may have 3 double bonds and 0 rings
C) it may have 1 triple bond and 3 rings
D) it may have 0 double bonds and 3 rings

42 How would the bond strength of the C:C double bond in an alkene compare to that of a C:C single bond in the corresponding alkane?
A) The double bond would have the same strength as the single bond.
B) The double bond would be stronger than, but less than twice as strong as the single bond.
C) The double bond would have exactly twice the strength of the single bond.
D) The double bond would have more than twice the strength of the single bond.

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43 Which of the following cations is most stable?
A) FH2+
B) OH3+
C) NH4+
D) CH5+

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44 The toxic environmental pollutant dioxin is 44.8% carbon, 1.25% hydrogen and 44.0% chlorine. Its molecular weight is 320±10
What is the molecular formula of dioxin?
A) C10H8O4Cl4
B) C12H6O2Cl4
C) C6H2OCl2
D) C12H4O2Cl4

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45 Which of the following covalent compounds does not have any formally charged atoms?
A) (CH3)3NO
B) CH2=N=N
C) CH3-O-N=O
D) CH3C≡NO

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46 Which of the following statements is not generally correct?
A) endothermic reactions have larger energies of activation than exothermic reactions
B) the rate of a reaction is proportional to its activation energy
C) the rate of a reaction generally increases as the temperature is raised
D) all reactions in which bonds are broken and formed have a significant activation energy

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47 Which of the following compounds has no isomer?
A) CH3CH2CH2Cl
B) CH3CHO
C) CH2=CHCl
D) ClCH2CH2Cl

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48 Which of the following statements about carbon is not correct?
A) carbon forms strong covalent bonds to itself, allowing chains and rings to be made.
B) carbon expands its valence shell to accomodate more than eight electrons and thus forms double and triple bonds.
C) carbon forms strong covalent bonds to elements like nitrogen and oxygen because it does not have lone pairs of valence electrons to destabilize the bonds.
D) carbon and hydrogen have similar electronegativity and form strong bonds to each other, thus avoiding the high reactivity shown by metal hydrides.

27 Which compound does not react with ammonia to form propanamide under mild conditions?
A) propanoic acid
B) propanoyl chloride
C) ethyl propanoate
D) propanoic anhydride

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28 Which sequence of reactions would be best for the conversion of toluene into para-bromophenylacetic acid.? ( NBS = N-bromosuccinimide )
A) i) Br2 & FeBr3; ii) KMnO4 & heat; iii) NaCN in ethanol; iv) H3O(+) & heat
B) i) Br2 & FeBr3; ii) NBS in CCl4; iii) Mg in ether followed by CO2; iv) H3O(+)
C) i) Br2 & FeBr3; ii) NBS in CCl4; iii) NaCN in ethanol; iv) H3O(+) & heat
D) i) Br2 & FeBr3; ii) KMnO4 & heat; iii) Mg in ether followed by CO2; iv) H3O(+)

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29 On heating in the presence of bromine, 2,2-dimethyl-3-oxobutyric acid produces 3-bromo-3-methyl-2-butanone.
What unstable intermediate is involved in this reaction?
A) 1,2,2-trimethylcyclopropanol
B) 2,2-dimethyl β butyrolactone
C) 2-hydroxy-3-methylbutene
D) dimethylketene

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30 Fischer esterification of mesitoic acid ( 2,4,6-trimethylbenzoic acid ) is extremely slow compared with benzoic acid itself.
What is the major factor accounting for this difference in reactivity?
A) steric hindrance by the ortho methyl groups.
B) the electron donating inductive effect of the methyl substituents.
C) acid-catalyzed rearrangement of the methyl substituents.
D) rapid acid-catalyzed decarboxylation of mesitoic acid.

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31 Which of the following reagents would be best for reducing an ester to an aldehyde?
A) LiAlH4 in ether
B) B2H6 in ether
C) NaBH4 in aqueous ethanol
D) diisobutylaluminum hydride (DIBAH) in toluene at -78 ºC

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32 Which of the following reagents are suitable for reducing an amide to an aldehyde? I LiAlH4 in ether II diisobutylaluminum hydride (DIBAH) in toluene at -78 ºC
III LiAlH(t-C4H9O)3 in ether at -78 ºC IV NaBH4 in aqueous ethanol

A) I & IV
B) II & III
C) only I
D) all but III are suitable

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33 Which of the following reagents are suitable for reducing an acyl chloride to an aldehyde? I LiAlH4 in ether II NaBH4 in tert-butanol
III LiAlH(t-C4H9O)3 in ether at -78 ºC IV H2 and Pd/BaSO4 catalyst

A) III & IV
B) I & IV
C) only I
D) all are suitable

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34 Which of the following methods would not be useful for preparing ketones? I Friedel-Crafts reaction of an acyl chloride with benzene (AlCl3 catalysis)
II reaction of R2CuLi with an acyl chloride in ether at low temperature.
III reaction of Grignard reagents with nitriles, followed by hydrolysis
IV reaction of methyllithium with the lithium salt of a carboxylic acid, followed by hydrolysis
A) II & IV
B) II & III
C) only III
D) none (all are useful)

36 Which of the following reactions is most likely to produce ethyl propanoate?
A) sodium ethoxide + propanoic acid
B) propanol + acetyl chloride
C) sodium propanoate + acetic anhydride
D) potassium propanoate + ethyl iodide

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37 If diethyl amine is treated separately with the following derivatives of isobutyric acid, what order of reactivity is expected?
greater reactivity > lesser reactivity I isobutyronitrile
( 2-methylpropanenitrile ) II isobutyryl chloride
( 2-methylpropanoly chloride ) III ethyl isobutyrate IV isobutyric anhydride
( 2-methylpropanoic anhydride )
A) I > II > III > IV
B) II > IV > III > I
C) IV > II > III > I.
D) IV > III > II > I

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38 Methyl esters of carboxylic acids, RCO2CH3, have somewhat higher molecular masses than 1 º-amide, RCONH2, derivatives of the same acid.
However, the amides have much higher boiling points. What is responsible for this difference?
A) hydrogen bonding
B) resonance conjugation of N with C=O
C) the lower electronegativity of N versus O
D) rapid pyramidal inversion of the nitrogen

42 How would the bond strength of the C:C double bond in an alkene compare to that of a C:C single bond in the corresponding alkane?
A) The double bond would have the same strength as the single bond.
B) The double bond would be stronger than, but less than twice as strong as the single bond.
C) The double bond would have exactly twice the strength of the single bond.
D) The double bond would have more than twice the strength of the single bond.

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43 Which of the following cations is most stable?
A) FH2+
B) OH3+
C) NH4+
D) CH5+

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44 The toxic environmental pollutant dioxin is 44.8% carbon, 1.25% hydrogen and 44.0% chlorine. Its molecular weight is 320±10
What is the molecular formula of dioxin?
A) C10H8O4Cl4
B) C12H6O2Cl4
C) C6H2OCl2
D) C12H4O2Cl4

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45 Which of the following covalent compounds does not have any formally charged atoms?
A) (CH3)3NO
B) CH2=N=N
C) CH3-O-N=O
D) CH3C≡NO

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46 Which of the following statements is not generally correct?
A) endothermic reactions have larger energies of activation than exothermic reactions
B) the rate of a reaction is proportional to its activation energy
C) the rate of a reaction generally increases as the temperature is raised
D) all reactions in which bonds are broken and formed have a significant activation energy

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47 Which of the following compounds has no isomer?
A) CH3CH2CH2Cl
B) CH3CHO
C) CH2=CHCl
D) ClCH2CH2Cl

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48 Which of the following statements about carbon is not correct?
A) carbon forms strong covalent bonds to itself, allowing chains and rings to be made.
B) carbon expands its valence shell to accomodate more than eight electrons and thus forms double and triple bonds.
C) carbon forms strong covalent bonds to elements like nitrogen and oxygen because it does not have lone pairs of valence electrons to destabilize the bonds.
D) carbon and hydrogen have similar electronegativity and form strong bonds to each other, thus avoiding the high reactivity shown by metal hydrides

21 Which of the following compounds has a C-H bond with the lowest bond dissociation energy?
A) C2H6
B) C6H6
C) C2H2
D) CH3CH=CH2

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22 In order for a reagent to behave as a nucleophile it must have ...
A) an overall positive charge.
B) an overall negative charge.
C) a non-bonding electron pair.
D) a nitrogen or sulfur atom.

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23 The H–C–O bond angle in H2C=O (formaldehyde) is approximately .....
A) 90º
B) 109º.
C) 120º.
D) 180º.

Which of the following is a correct name for (CH3)2C=CHCOCH3?
A) 2-methyl-2-penten-4-one
B) 4-methyl-3-penten-2-one
C) 1,3-dimethyl-2-pentenal
D) isopentenone

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2. Which of the following is 3,3-diphenylpropanal?
A) C6H5CH2CH(C6H5)CHO
B) C6H5CH2CH2COC6H5
C) (C6H5)2CHCH2CHO
D) (C6H5)2CHCH2COC6H5

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3. Which of the following compounds is not named correctly? A) 2-methyl-3-heptanone (CH3)2CHCOCH2CH2CH2CH3
B) phenylacetaldehyde C6H5CH2CHO
C) 4-hexyn-2-one CH3COCH2C≡CCH3
D) para-bromoacetophenone p-BrC6H4CH2COCH3

9 Which of the following statements is not generally true?
A) C=O is stronger than an equivalent C=C
B) C=O has a larger bond dipole than C=C
C) aldehydes and ketones have higher boiling points than similarly sized alkenes
D) alkenes add nucleophiles more rapidly than aldehydes or ketones of similar structure

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10 Which of the following compounds exchanges the largest number of hydrogens for deuterium when treated with KOD in D2O?
A) 3-methyl-1,2-cycloheptanedione
B) 2-methyl-1,3-cycloheptanedione
C) 5-methyl-1,3-cycloheptanedione
D) 6-methyl-1,4-cycloheptanedione

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11 Four C8H14O ketones are examined by 13Cnmr spectroscopy.
One of them has five distinct carbon signals. Which of the following fits this fact?
A) 4,4-dimethylcyclohexanone
B) 3,3-dimethylcyclohexanone
C) 2,2-dimethylcyclohexanone
D) 2,2,4,4-tetramethylcyclobutanone

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12 Which of the following compounds could not be converted to pentanal in one or two steps?
A) 1-pentyne
B) trans-5-decene
C) 2-pentanone
D) 1-pentanol

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13 Treatment of cyclohexanone with an excess of H218O produces 18O labeled cyclohexanone.
Which of the following is a likely intermediate in this isotope exchange? (the isotope is not named)
A) 1-cyclohexen-1-ol
B) 1,1-cyclohexanediol
C) 2-cyclohexen-1-one
D) 1,2-cyclohexanediol

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14 Reaction of C6H5CHBr2 with NaOH in aqueous THF is likely to produce which product?
A) C6H5CHBrOH
B) C6H5CH(OH)2
C) C6H5CHO
D) C6H5CO2H

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15 Which of the following carbonyl compounds reacts most rapidly with nucleophilic reagents?
A) benzaldehyde
B) 3,3-dimethylbutanal
C) acetophenone
D) 2,2-dimethylcyclohexanone

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16 Which of the following amines would be best chosen for preparing an enamine derivative from cyclohexanone?
A) dimethylamine
B) ethylamine
C) trimethylamine
D) hydroxylamine

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17 Which reaction or sequence of reactions would best accomplish the following synthesis?

A) CH3NH2, acid catalyst & heat
B) CH2=NH, acid catalyst & heat
C) (i) NH3 acid catalyst & heat; (ii) CH2I2 & Zn(Cu)
D) (i) HCN & NaCN; (ii) LiAlH4 in ether

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18 Heating cyclopentanone with either: I ethyl amine, or II diethylamine, together with an acid catalyst leads to different results.
Which of the following best describes this difference?
A) I gives an imine & II fails to react
B) I gives an enamine & II fails to react
C) I gives an imine & II gives an enamine
D) I gives an enamine & II gives an imine

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19 Which reaction or sequence of reactions would be best used to convert cyclohexanone to cis-1,2-cyclohexanediol?
A) PCC in CH2Cl2 and base
B) (i) NaBH4; (ii) H3PO4 & heat; (iii) OsO4 in pyridine
C) (i) NaBH4; (ii) H3PO4 & heat; (iii) C6H5CO3H
D) (i) NaBH4; (ii) OsO4 in pyridine

23 Which of the following reaction sequences would be best for converting cyclohexanol to methylenecyclohexane, (CH2)5C=CH2 ?
A) (i) H3PO4 & heat; (ii) CH2I2 + Zn(Cu)
B) (i) PCC in CH2Cl2; (ii) CH3MgBr; (iii) H3PO4 & heat
C) PCC in CH2Cl2; (ii) (C6H5)3P=CH2
D) CH2N2 & heat

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24 Which of the following Wittig reagents would be useful for converting R2C=O into R2CHCH=O?
A) (C6H5)3P=CH-OCH3
B) (C6H5)3P=CH-CH3
C) (C6H5)3P=Cl2
D) (C6H5)3P=CH-CH=CH2

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25 Two equivalents of the Wittig reagent (CH3)2C=CH-CH=P(C6H5)3 were allowed to react with a C4H4O2 compound.
The chief product was 2,11-dimethyl-2,4,6,8,10-dodecapentaene, (CH3)2C=CH(CH=CH)3CH=C(CH3)2.
What was the C4H4O2 compound used in this reaction?
A) 2-butyne-1,4-diol
B) 1,2-cyclobutanedione
C) 1,3-butadien-2,3-diol
D) 2-butenedial

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26 Which of the following reactions would not be a useful way of preparing 1-phenyl-2-butanol?
A) phenylacetaldehyde + ethylmagnesium bromide
B) butanal + phenylmagnesium bromine
C) propanal + benzylmagnesium bromine
D) 1-phenyl-2-butanone + NaBH4

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27 Which of the following reactions would not be a useful way of preparing 2-phenyl-2-butanol?
A) 2-butanone + phenylmagnesium bromine
B) acetophenone + ethylmagnesium bromide
C) cis-2,3-dimethyloxirane + phenylmagnesium bromide
D) ethylphenylketone + methylmagnesium iodide

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28 In the reaction of (R)-3-phenyl-2-butanone with methylmagnesium iodide, what happens to the configuration of the stereogenic center?
A) nothing, it remains unchanged
B) inversion takes place
C) racemization occurs
D) the product is achiral

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29 Which of the following reactions would not be useful for converting 4,4-diethylcyclohexanone into 1,1-diethylcyclohexane?
A) Wolff-Kishner reduction (N2H4, strong base & heat)
B) Clemmensen reduction (Zn/Hg, acid & heat)
C) thioacetal reduction (i HSCH2CH2SH & BF3; ii H2 + Raney Ni)
D) LiAlH4 in THF & heat

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30 Which of the following is a semicarbazone derivative of an aldehyde (RCHO)?
A) RCH=N-NHCONH2
B) RCH=N-OH
C) RCH=N-NH2
D) RCH=N-C(CH3)3

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31 Which of the following isomers is most acidic ?
A) 3,4-hexanedione
B) 2,5-hexanedione
C) 2,4-hexanedione
D) hexanedial

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32 You have two C6H10O ketones, I and II. Both are optically active, but I is racemized by treatment with base and II is not.
Wolff-Kishner reduction of both ketones gives the same achiral hydrocarbon, formula C6H12.
What reasonable structures may be assigned to I and II?
A) I is 3-methyl-4-penten-2-one; II is 4-methyl-1-penten-3-one
B) I is 2-methylcyclopentanone; II is 3-methylcyclopentanone
C) I is 3-methylcyclopentanone; II is 2-methylcyclopentanone
D) I is 2-ethylcyclobutanone; II is 3-ethylcyclobutanone

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33 Jones' reagent oxidizes aldehydes to carboxylic acids but normally does not oxidize ketones.
What intermediate species is most likely responsible for the aldehyde oxidation?
A) a carbonyl hydrate
B) an enol tautomer
C) an oxonium conjugate acid of the aldehyde
D) an acylium cation

42 Base induced elimination of 3-chlorocyclohexanone I is much faster than elimination of cyclohexyl chloride II.
What is the major factor accounting for this difference?
A) the halogen in I is less hindered
B) the halogen in I is forced to be axial
C) elimination of I produces a more stable conjugated double bond
D) I rapidly forms an enolate anion, and this immediately eliminates a stable chloride ion

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43 Which of the following optically active compounds will be racemized on treatment with warm alcoholic sodium ethoxide?
(R)-2,2,6-trimethylcyclohexanone (R)-2,2,5-trimethylcyclohexanone (R)-2-methyl-2-phenylcyclohexanone (R)-4-methyl-2-cyclohexen-1-one
I II III IV
A) I and II
B) I and III
C) I and IV
D) all compounds will be racemized

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44 A C5H8 hydrocarbon is reacted with BH3 in THF, followed by oxidation with alkaline hydrogen peroxide.
Treatment of the resulting product with PCC in CH2Cl2 produces a chiral ketone, formula C5H8O.
What hydrocarbon best fits these facts?
A) 1-methylcyclobutene
B) methylenecyclobutane
C) vinylcyclopropane
D) cyclopentene

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45 Which of the following compounds would not be a possible product from the mixed aldol reaction of acetaldehyde and butanal?
A) 3-hydroxybutanal
B) 2-ethyl-3-hydroxybutanal
C) 3-ethyl-2-hydroxyhexanal
D) 3-hydroxyhexanal

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46 A C7H12O2 compound gives a positive Tollens' silver mirror test and a positive iodoform test.
Which of the following would satisfy these facts?
A) 2-hydroxy-3,3-dimethylcyclopentanone
B) 2,5-heptanedione
C) 2,2-dimethyl-3-oxopentanal
D) 2,2-dimethyl-4-oxopentanal

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47 The iodoform test for methyl ketones is not widely used anymore.
Which of the following spectroscopic tools is best for providing equivalent information?
A) UV-Visible
B) 1H nmr
C) 13C nmr
D) infrared

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48 An aldol condensation is used to prepare 1,3-diphenyl-2-propenone, C6H5CH=CHCOC6H5.
Which combination of reactants will lead to this product?
A) enolate donor=acetaldehyde; carbonyl acceptor=benzaldehyde
B) enolate donor=phenylacetaldehyde; carbonyl acceptor=phenylacetaldehyde
C) enolate donor=acetophenone; carbonyl acceptor=benzaldehyde
D) enolate donor=propiophenone; carbonyl acceptor=benzaldehyde

53 2,2-Dimethyl-1,3-propanediol is coveniently prepared by heating 2-methylpropanal with excess formaldehyde and Ca(OH)2.
What sequence of reactions takes place in this synthesis?
A) dehydrogenation to 2-methyl-2-propenal followed by addition of formaldehyde
B) dehydrogenation to dimethylketene followed by addition of formaldehyde
C) a crossed aldol reaction followed by a crossed Cannizzaro reaction
D) a crossed Cannizzaro reaction followed by a crossed aldol reaction