CHEM10050 - Gilheany Lecture 8 : Alkenes

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1
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Which statement about alkenes is true?

a) They have fewer hydrogens than the corresponding alkanes.

b) They have more hydrogens than the corresponding alkanes.

c) They have the same number of hydrogens as the corresponding alkanes.

a) They have fewer hydrogens than the corresponding alkanes.

2
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Which type of bond is common in natural and commercial substances?

a) Single bonds

b) Double bonds

c) Triple bonds

b) Double bonds

3
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How are alkenes named in comparison to alkanes?

a) Alkenes are named differently than alkanes.

b) Alkenes are named in the same way as alkanes.

c) Alkenes are named by reversing the order of the carbon chain.

b) Alkenes are named in the same way as alkanes.

4
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What is the function of ethylene?

a) It promotes ripening of fruit.

b) It promotes growth of roots.

c) It promotes flowering of plants.

a) It promotes ripening of fruit.

5
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What is the largest volume chemical produced per annum?

a) Ethylene

b) Propylene

c) Methane

a) Ethylene

6
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Which compound is a precursor for polypropylene?

a) Ethylene

b) Propylene

c) Butylene

b) Propylene

7
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What are terpenes?

a) Compounds whose formulae are multiples of ethene

b) Compounds whose formulae are multiples of isoprene

c) Compounds whose formulae are multiples of propane

b) Compounds whose formulae are multiples of isoprene

8
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What are terpenoids?

a) Modified versions of terpenes containing oxygen or other elements

b) Compounds whose formulae are multiples of terpenes

c) Modified versions of terpenes containing only carbon and hydrogen

a) Modified versions of terpenes containing oxygen or other elements

9
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What is the main component of essential oils obtained by steam distillation of plants?

a) Alkanes

b) Alkenes

c) Terpenoids

c) Terpenoids

10
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Which compound is an example of a monoterpene?

a) Ethylene

b) Limonene

c) Propylene

b) Limonene

11
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What is a polyene?

a) A compound with many C-C bonds

b) A compound with many C-O bonds

c) A compound with many C-H bonds

a) A compound with many C-C bonds

12
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What is the function of terpenes and terpenoids?

a) To promote ripening of fruit

b) To give plants a pleasant odor

c) To produce polyethylene

b) To give plants a pleasant odor

13
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What is the name of the alkene hormone that promotes ripening of fruit?

a) Ethylene

b) Propylene

c) Methane

a) Ethylene

14
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What is the precursor for polypropylene?

a) Ethylene

b) Propylene

c) Methane

b) Propylene

15
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What is the colour of b-carotene?

a) Orange

b) Red

c) Green

a) Orange

16
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What is the hybridization of carbon atoms in alkenes?

a) sp

b) sp2

c) sp3

b) sp2

17
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How is the weaker p bond formed in the C=C double bond?

a) By end-on overlap of two sp2 hybrid orbitals

b) By side-on overlap of the p orbitals

c) By end-on overlap of two p orbitals

b) By side-on overlap of the p orbitals

18
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What is the abbreviation for the phenyl fragment C6H5?

a) Ph

b) Me

c) Et

a) Ph

19
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What is the difference between E and Z isomers of disubstituted alkenes?

a) They have different functional groups

b) They have different numbers of double bonds

c) They have different spatial arrangements of substituents

c) They have different spatial arrangements of substituents

20
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How many stereoisomers are possible for disubstituted alkenes?

a) One

b) Two

c) Three

b) Two

21
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What is the purpose of the Cahn-Ingold-Prelog sequence rules in alkene nomenclature?

a) To assign priorities to the two substituents on each carbon of the alkene.

b) To identify the cis or trans isomer of the alkene.

c) To determine the hybridization of the alkene carbons.

d) To calculate the melting point of the alkene.

a) To assign priorities to the two substituents on each carbon of the alkene.

22
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What is the meaning of (E) in alkene nomenclature?

a) entgegen (against)

b) zusammen (together)

c) cis (same side)

d) trans (opposite side)

a) entgegen (against)

23
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What is the meaning of (Z) in alkene nomenclature?

a) entgegen (against)

b) zusammen (together)

c) cis (same side)

d) trans (opposite side)

b) zusammen (together)

24
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When naming tri- and tetrasubstituted alkenes, what method must be used to avoid ambiguity?

a) Lewis structure

b) VSEPR theory

c) Cahn-Ingold-Prelog sequence rules

d) Bonding orbital theory

c) Cahn-Ingold-Prelog sequence rules

25
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Which of the following is always true of cis isomers compared to trans isomers?

a) They always have the higher melting point.

b) They always have the lower melting point.

c) They are often crystalline.

d) They are usually an oil.

b) They always have the lower melting point.

26
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Which of the following is often true of trans isomers compared to cis isomers?

a) They always have the higher melting point.

b) They always have the lower melting point.

c) They are often crystalline.

d) They are usually an oil.

c) They are often crystalline.

27
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What type of double bond rotation is prevented in alkenes?

a) S-S bond rotation

b) C-O bond rotation

c) C-C bond rotation

d) C=C bond rotation

d) C=C bond rotation

28
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What is the result of promoting electron from p to p* orbital in a cis isomer?

a) The double bond rotates.

b) The double bond is locked in place.

c) The melting point decreases.

d) The melting point increases.

a) The double bond rotates.

29
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What is the abbreviated form for the phenyl fragment C6H5?

a) Me

b) Et

c) Ph

d) Bu

c) Ph

30
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Which compound contains 11 conjugated C=C bonds and is orange?

a) b-carotene

b) limonene

c) stilbene

d) propylene

a) b-carotene

31
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What is the basis of vision?

a) 11-cis-retinal

b) Retinol

c) Vitamin A

d) b-carotene

a) 11-cis-retinal

32
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What is the change in shape of the polyene responsible for in vision?

a) Absorption of light

b) Conversion from cis to trans form

c) Signal to the brain

d) All of the above

c) Signal to the brain

33
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Which type of isomerism is involved in vision?

a) Cis/trans isomerism

b) Optical isomerism

c) Geometric isomerism

d) Structural isomerism

a) Cis/trans isomerism

34
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Which of the following is NOT an electrophile in the electrophile diagram?

a) H-X

b) Alcohols

c) Acids

d) Br2

b) Alcohols

35
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Which of the following statements is true about the relative reactivity of nucleophiles and electrophiles?

a) Alkenes are above acids in the electrophile diagram

b) Nucleophiles will react with electrophiles that are above them in the electrophile diagram

c) We cannot make any predictions about the feasibility of reactions using the electrophile diagram

d) None of the above

b) Nucleophiles will react with electrophiles that are above them in the electrophile diagram

36
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What is the most characteristic reaction of alkenes?

a) Elimination

b) Substitution

c) Addition

d) Rearrangement

c) Addition

37
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What type of bond is broken in addition reactions of alkenes?

a) S bond

b) P bond

c) Both S and P bonds

d) None of the above

b) P bond

38
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Which of the following reagents can add to alkenes?

a) H-H

b) H-Cl

c) Cl-Cl

d) All of the above

d) All of the above

39
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Which reagent addition to alkenes will be discussed in detail?

a) H-H

b) H-Cl

c) Cl-Cl

d) Br-Br

b) H-Cl

40
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What remains after addition reactions involving p MO?

a) Both S and P bonds

b) S bond

c) P bond

d) None of the above

b) S bond

41
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What is the first step in the addition of HCl to alkenes?

a) H-Cl dissociates into H+ and Cl- ions.

b) The chloride ion is attracted to the carbocation.

c) Both of the electrons from the p bond move to from a new bond between the H+ and one carbon of the alkene.

d) One of the lone pairs of electrons on the chloride ion moves to form a new C—Cl bond.

c) Both of the electrons from the p bond move to from a new bond between the H+ and one carbon of the alkene.

42
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What is a carbocation?

a) A molecule that can act as both an electrophile and a nucleophile.

b) A molecule that has a positive charge on one carbon atom.

c) A molecule that has a negative charge on one carbon atom.

d) A molecule that has no double bonds between its carbon atoms.

b) A molecule that has a positive charge on one carbon atom.

43
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What is the role of the alkene in the addition of HCl to alkenes?

a) To act as an electrophile.

b) To act as a nucleophile.

c) To provide the chloride ion.

d) To provide the hydrogen ion.

b) To act as a nucleophile.

44
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What happens to the carbocation in the addition of HCl to alkenes?

a) It is destroyed.

b) It is converted into an alkene.

c) It attracts the chloride ion.

d) It becomes a nucleophile.

c) It attracts the chloride ion.

45
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Why is the carbocation a highly reactive, highly electrophilic species?

a) Because it has a negative charge.

b) Because it has a positive charge.

c) Because it has a double bond.

d) Because it has a lone pair of electrons.

b) Because it has a positive charge.

46
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Which of the following is a characteristic of the hydrogen ion in the addition of HCl to alkenes?

a) It contains zero electrons.

b) It is a nucleophile.

c) It is attracted to the carbocation.

d) It is a weak acid.

a) It contains zero electrons.

47
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What is the second step in the addition of HCl to alkenes?

a) The addition of HCl to the carbocation.

b) The dissociation of H-Cl into H+ and Cl- ions.

c) The formation of a new C—H bond.

d) The attraction of the chloride ion to the carbocation.

d) The attraction of the chloride ion to the carbocation.

48
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What is the role of the chloride ion in the addition of HCl to alkenes?

a) To act as an electrophile.

b) To act as a nucleophile.

c) To provide the hydrogen ion.

d) To provide the alkene.

b) To act as a nucleophile.

49
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What is the curly arrow notation used for in the addition of HCl to alkenes?

a) To show the movement of electrons in a reaction.

b) To show the movement of protons in a reaction.

c) To show the formation of a new C—Cl bond.

d) To show the dissociation of H-Cl into H+ and Cl- ions.

a) To show the movement of electrons in a reaction.

50
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Which of the following is a characteristic of carbocation intermediates?

a) They have a negative charge.

b) They are highly stable.

c) They have a positive charge.

d) They are highly nucleophilic.

c) They have a positive charge.

51
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What is the typical energy profile for a two-step reaction?

a) The final products have higher energy than the starters.

b) The carbocation intermediate has much lower energy than the starting materials.

c) The energy difference between the products and the reactants is the activation energy barrier.

d) The products form because they are less stable than the reactants.

c) The energy difference between the products and the reactants is the activation energy barrier.

52
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What is the determinant of the rate of reaction in a two-step reaction?

a) The size of the activation energy barrier.

b) The stability of the carbocation intermediate.

c) The stability of the reactants.

d) The size of the free energy of reaction.

a) The size of the activation energy barrier.

53
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What is the rate-determining step in the addition of HCl to unsymmetrical alkenes?

a) Formation of the product.

b) Formation of the carbocation intermediate.

c) Formation of the chloride ion.

d) Dissociation of HCl into H+ and Cl-.

b) Formation of the carbocation intermediate.

54
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What is the general trend for the stability order of carbocations?

a) Tertiary is much less stable than secondary, which is much less stable than primary.

b) Tertiary is much more stable than secondary, which is much more stable than primary.

c) Primary is much more stable than secondary, which is much more stable than tertiary.

d) Primary is much less stable than secondary, which is much less stable than tertiary.

b) Tertiary is much more stable than secondary, which is much more stable than primary.

55
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What is the product of the addition of HCl to 2-methylpropene?

a) The chloride ion attaches to the carbon with fewer alkyl substituents.

b) The hydrogen attaches to the carbon with fewer alkyl substituents.

c) The chloride ion attaches to the carbon with more alkyl substituents.

d) The hydrogen attaches to the carbon with more alkyl substituents.

d) The hydrogen attaches to the carbon with more alkyl substituents.

56
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What is Markovnikov's Rule?

a) The hydrogen attaches to the carbon with fewer alkyl substituents.

b) The hydrogen attaches to the carbon with more alkyl substituents.

c) The chloride ion attaches to the carbon with fewer alkyl substituents.

d) The chloride ion attaches to the carbon with more alkyl substituents.

b) The hydrogen attaches to the carbon with more alkyl substituents.

57
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What is the usefulness of the addition of HX to alkenes?

a) Useful only if primary carbocations are formed.

b) Useful only if secondary carbocations are formed.

c) Useful only if tertiary carbocations are formed.

d) Not useful at all.

c) Useful only if tertiary carbocations are formed.

58
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What are alkyl groups?

a) Electrophilic groups.

b) Nucleophilic groups.

c) Groups that donate electrons.

d) Groups that accept electrons.

c) Groups that donate electrons.

59
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What is the effect of alkyl groups on the stability of carbocations?

a) Alkyl groups destabilize carbocations.

b) Alkyl groups have no effect on the stability of carbocations.

c) Alkyl groups stabilize carbocations.

d) Alkyl groups make carbocations more electrophilic.

c) Alkyl groups stabilize carbocations.

60
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What is the product of the addition of HCl to symmetrical alkenes?

a) Only one

b) Two possible products.

c) None.

d) Depends on the reaction conditions.

a) Only one.

61
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What is the major difference between addition of HX and addition of bromine to alkenes?

a) Addition of HX results in anti addition, while addition of bromine results in syn addition.

b) Addition of HX involves the formation of a carbocation intermediate, while addition of bromine does not.

c) Addition of HX proceeds via an S N 2 reaction, while addition of bromine proceeds via an S N 1 reaction.

d) Addition of HX works for most alkenes, while addition of bromine works for only a few alkenes.

b) Addition of HX involves the formation of a carbocation intermediate, while addition of bromine does not.

62
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What is the result of the addition of two Br atoms to opposite sides of an alkene?

a) Syn addition

b) Anti addition

c) Markovnikov addition

d) No addition

b) Anti addition

63
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Why does hydrogenation require a transition metal catalyst?

a) The H-H bond is too weak to react with alkenes without the help of a catalyst.

b) The reaction involves a carbocation intermediate, which can only be stabilized by a catalyst.

c) The catalyst helps break the alkene double bond, allowing H atoms to be added.

d) The catalyst helps prevent the addition of more than two H atoms to the alkene.

c) The catalyst helps break the alkene double bond, allowing H atoms to be added.

64
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What type of addition occurs in the hydrogenation of alkenes?

a) Syn addition

b) Anti addition

c) Markovnikov addition

d) No addition

a) Syn addition

65
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Why does the addition of hydrogen to alkenes require a catalyst?

a) The reaction is exothermic and releases energy.

b) The H-H bond is too weak to react with alkenes without the help of a catalyst.

c) The reaction is endothermic and requires energy to proceed.

d) The reaction produces a large amount of unwanted side products.

b) The H-H bond is too weak to react with alkenes without the help of a catalyst.

66
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Which of the following is true of the addition of bromine to alkenes?

a) It works for only a few alkenes.

b) It involves the formation of a carbocation intermediate.

c) It results in syn addition.

d) It works for most alkenes.

d) It works for most alkenes.

67
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What type of reaction is the addition of hydrogen to alkenes?

a) S N 1

b) S N 2

c) Syn addition

d) Anti addition

c) Syn addition

68
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What is the mechanism of the addition of hydrogen to alkenes?

a) Complex

b) S N 1

c) S N 2

d) Straightforward

a) Complex

69
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What is the role of transition metals in the hydrogenation of alkenes?

a) To break the H-H bond and transfer H atoms to the alkene.

b) To stabilize carbocation intermediates.

c) To prevent unwanted side products from forming.

d) To promote the reaction without being consumed.

d) To promote the reaction without being consumed.

70
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Which of the following is a characteristic of the addition of bromine to alkenes?

a) It involves the formation of a carbocation intermediate.

b) It results in anti addition.

c) It only works for symmetrical alkenes.

d) It requires high temperatures and pressures.

b) It results in anti addition

71
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What is the result of addition of hundreds or thousands of alkene monomers?

a) Formation of polymers

b) Formation of small molecules

c) Formation of gases

d) Formation of liquids

a) Formation of polymers

72
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What are the resulting properties of polymers compared to the small molecules from which they are prepared?

a) They have similar properties

b) They have weaker properties

c) They have stronger properties

d) They have opposite properties

c) They have stronger properties

73
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What makes polymers strong materials?

a) The small size of the molecules

b) The long and entangled molecules

c) The lack of entanglement in the molecules

d) The presence of many double bonds

b) The long and entangled molecules

74
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What are the two important methods for the synthesis of alkenes?

a) Addition and substitution

b) Elimination and hydrogenation of alkynes

c) Reduction and oxidation

d) Hydrolysis and condensation

b) Elimination and hydrogenation of alkynes

75
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What are some examples of thermoplastics?

a) Glass, ceramics, and metals

b) Rubber and latex

c) Polyethylene, polypropylene, and PVC

d) Wood and paper

c) Polyethylene, polypropylene, and PVC

76
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What is the term used to describe the occurrence of alkenes as terpenes and terpenoids?

a) Aromaticity

b) Isomerism

c) Polymerization

d) Terpenicity

d) Terpenicity

77
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How can you assign the stereochemistry of simple alkenes?

a) By counting the number of double bonds

b) By measuring the bond angles

c) By assigning the E or Z configuration

d) By using mass spectrometry

c) By assigning the E or Z configuration

78
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How can you distinguish conjugated from non-conjugated polyenes?

a) By counting the number of double bonds

b) By measuring the bond angles

c) By the presence of alternating single and double bonds

d) By the presence of multiple functional groups

c) By the presence of alternating single and double bonds

79
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What is the difference between syn and anti addition?

a) Syn addition involves addition of two groups to the same side, while anti addition involves addition of two groups to opposite sides of the double bond.

b) Syn addition involves addition of two groups to opposite sides, while anti addition involves addition of two groups to the same side of the double bond.

c) Syn addition involves formation of carbocation intermediates, while anti addition does not.

d) Anti addition involves use of a catalyst, while syn addition does not.

a) Syn addition involves addition of two groups to the same side, while anti addition involves addition of two groups to opposite sides of the double bond.

80
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What is the purpose of using a catalyst in the hydrogenation of alkenes?

a) To increase the energy barrier for the reaction

b) To decrease the energy barrier for the reaction

c) To prevent the reaction from occurring

d) To change the stereochemistry of the product

b) To decrease the energy barrier for the reaction

81
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What is the mechanism involved in the addition of HCl to alkenes?

a) SN1

b) SN2

c) E1

d) E2

d) E2

82
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What is the name of the process that adds hundreds or thousands of alkene monomers to produce polymers?

a) Polymerisation

b) Elimination

c) Hydrogenation

d) Halogenation

a) Polymerisation

83
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Which of the following materials is not a polymer?

a) Polyethylene

b) Polypropylene

c) PVC

d) Methane

d) Methane

84
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What is the name of the method for the synthesis of alkenes that involves the elimination of a leaving group from a substrate?

a) Addition reaction

b) Hydrogenation

c) Elimination reaction

d) Halogenation

c) Elimination reaction

85
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What is the name of the method for the synthesis of alkenes that involves the hydrogenation of alkynes?

a) Addition reaction

b) Hydrogenation

c) Elimination reaction

d) Halogenation

b) Hydrogenation

86
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What is the difference between syn and anti addition?

a) Syn addition adds the two groups to the same side of the molecule, while anti addition adds the two groups to opposite sides.

b) Syn addition adds the two groups to opposite sides of the molecule, while anti addition adds the two groups to the same side.

c) Syn addition involves the formation of a carbocation intermediate, while anti addition does not.

d) Syn addition only works for certain types of alkenes, while anti addition works for most alkenes.

a) Syn addition adds the two groups to the same side of the molecule, while anti addition adds the two groups to opposite sides.