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Organic Chemistry > C14. Alkenes > Flashcards

C14. Alkenes Flashcards

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1
Q

What is stereoisomerism?

A

Same structural formula but different arrangement of atoms in space

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2
Q

What are the general structure of the alkene homologous group?

A

Hydrocarbons, unsaturated, contains C=C

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3
Q

What is the shape of an alkene?

A

Planar, 120 degree bonds

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4
Q

What are pi-bonds?

A

reactive part of a double bond formed above and below the plane of bonded atoms by sideways overlap of p-orbitals

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5
Q

How do alkenes use their electrons in the double bond?

A

3 electrons in formation of sigma-bond, 1 electron for formation of pi-bond

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6
Q

What are the bond enthalpy properties of double and single bonds?

A

Double bond (+612) is stronger than single bond (+347); Pi-bonds are weaker than sigma-bonds

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7
Q

What happens to the bonds of alkenes when they react?

A

Pi-bonds break, sigma-bonds stay intact

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8
Q

What are the difference between E/Z isomers?

A

Cis Isomer - Z; High priority groups are both on the bottom side or top side; Trans isomer - E; High priority groups are positioned diagonal across the double bond

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9
Q

What is the definition of E/Z isomers?

A

Type of stereoisomerism , different groups attach to each carbon of a C=C bond, may be arranged differently in space due to restricted rotation of C=C bond

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10
Q

What are the rules of the Cahn-Ingold-Prelog nomenclature system?

A

On each C=C, group with highest atomic number given priority; group with lowest atomic number is given lowest priority;

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11
Q

What are the criterias for E/Z isomers?

A

C=C double bond must be present; Each carbon must be attached to 2 different groups

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12
Q

What is a structural isomer?

A

Molecules have same molecular formula but different structural formula

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13
Q

What are the formulas for alkenes?

A

CnH2n

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14
Q

Why can a double bond not rotate? (restricted rotation)

A

2 p orbitals that overlap, forming a cloud of electron density above and below C=C bond, (pi-bond),

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15
Q

What are position isomers?

A

Isomers with the functional group in different positions

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16
Q

What are geometrical isomers?

A

Form of stereoisomerism due to restricted rotation, Trans, Cis

17
Q

What are the physical properties of alkenes?

A

Double bond does not greatly affect boiling of melting points; Physical properties are very similar to alkanes; Not soluble in water

18
Q

How reactive are alkenes and why?

A

More reactive than alkanes; C=C forms electron rich areas above and below the double bond, these regions are easily attacked by electrophiles; most alkene reactions are electrophilic addition

19
Q

What are the mechanisms for electrophilic addition?

A

Electrophile attracted to double bond; Positively charged electrophiles accept pair of electrons from =; Carbocation formed; negatively charged ion forms bond with carbocation

20
Q

What is a carbocation?

A

Positively charged carbon ion (ion that would be attracted to cathode)

21
Q

What is the positive inductive effect?

A

Alkyl groups have a tendency to release electrons ( represented by arrow along bonds showing direction)

22
Q

What is a tertiary carbocation?

A

Carbocation that draws electron density from 3 alkyl groups; Most stable

23
Q

What is a secondary carbocation?

A

Carbocation that draws electron density from 2 alkyl groups; More stable than primary

24
Q

What is a primary carbocation?

A

Carbocation that draws electron density form 1 alkyl group; Least stable carbocation

25
Q

How do stability of carbocations affect produce?

A

More stable carbocations will create more products

26
Q

What are electrophiles?

A

Electron pair acceptor; Atom that is attracted to a region of high electron density

27
Q

What are nucleophiles?

A

Electron rich species; Electron pair donors

28
Q

How do you test for the presence of carbon double bonds?

A

Addition reaction; bromine solution/bromine water is decolourised in presence of C=C double bonds

29
Q

What are the 2 steps for addition reactions of an alkene?

A

Formation of cation by electrophilic addition; Rapid reaction with negative ion (anion)

30
Q

What are polymers?

A

Compound comprising very large molecules that are multiples of simpler chemical units called monomers

31
Q

What is addition polymerisation?

A

Reaction in which many unsaturated alkene molecules bond together forming a very long saturated polymer chain

32
Q

What is a repeat unit?

A

Specific arrangement of atoms that occur repeatedly in a structure

33
Q

What are the properties of addition polymers?

A

Unreactive with substance placed inside; Durable; Do not break down naturally

34
Q

What is a biodegradable material?

A

Material that is broken down naturally in the environment by living organisms

Organic Chemistry (9 decks)

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