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IB Chemistry HL > 10. Organic Chemistry > Flashcards

10. Organic Chemistry Flashcards

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1
Q

Structural Isomers

A

same molecular formula, different structure

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2
Q

Alkanes

A

Alkyl Group

CnH2n+2

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3
Q
A

Alkenyl (Alkenes)

CnH2n

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4
Q
A

Alkynyl (Alkynes)

CnH2n-2

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5
Q

Saturated Hydrocarbons

A

Hydrocarbons that contain no double/ triple bonds (alkanes)

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6
Q

Unsaturated Hydrocarbons

A

Hydrocarbons that contain double/ triple bonds - Alkenes or Alkynes

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7
Q

R - X

X = F, Cl, Br, I

A

Halogenoalkanes

CnH2n+1X

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8
Q

R - O-H

A

Hydroxyl

suffix: -ol

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9
Q

R - O - R’

A

Ether

midfix: -oxy-

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10
Q
A

Aldehyde

suffix: -al

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11
Q
A

Carbonyl (Ketones)

suffix: -one

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12
Q
A

Ester

suffix: -oate

naming:

  • first part is from the alcohol group
  • second part is from the acid
  • add -oate
  • eg methyl ethanoate
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13
Q
A

Carboxyl (Carboxylic Acids)

suffix: -oic acid

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14
Q
A

Amino (Amines)

suffix: -amine

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15
Q
A

Carboxamide (Amides)

suffix: -amide

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16
Q
A

Cyano (Nitriles)

suffix: -nitrile

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17
Q
A

Phenyl (Arenes)

eg Benzene

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18
Q

Chemical Properties of Benzene

A
  • Due to resonance energy/ stabilization energy of benzene, it is reluctant to undergo addition reactions but will undergo substitution reactions
  • Delocalization minimizes the repulsion between electrons
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19
Q

Physical Characteristics of the Functional Groups

A
  • volatile if
    • small molecular weight
    • non polar
  • soluble if
    • small molecular weight
    • polar
  • branching
    • criss cross - less surface area > lower boiling point
    • zig zag - more contact/ surface area > higher boiling point
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20
Q

(Alkane Reactions)

Chemical Properties

A
  • Catenation is the ability to form bonds between atoms of the same element
    • Carbon is able to form strong covalent bonds
  • Fairly unreactive
  • Relatively strong, almost non-polar, single covalent bonds
  • Have no real sites that will encourage substances to attack them
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21
Q

(Alkane Reactions)

Combustion Reactions

A

Complete Combustion

CH4(g) + 2O2(g) –> CO2(g) + 2H2O(l)

Incomplete Combustion

CH4(g) + 1.5O2<strong>(g)</strong> –> CO(g) + 2H2O(l)

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22
Q

Homolytic Fission

A
  • Equal splitting
  • produces radicals

X : Y –> X• + Y•

  • If several bonds are present the weakest bond is broken first
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23
Q

Heterolytic Fission

A
  • Formation of a carbocation and a negative ion due to carbon losing it’s shared electron
  • Unequal splitting
  • Produces ions

X : Y –> X:- + Y+

X : Y –> X+ + Y:-

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24
Q

(Alkane Reactions)

Substitution Reactions

Methane + Cl2

A
  • Initiation - during initiation the weakest bond is broken as it requires less energy
    • H-C = 412; C-C = 348; Cl-Cl = 242
    • Cl-Cl –> Cl• + •Cl
  • Propagation - must start & end with a radical
    • Cl• + H-CH3 –> Cl-H + •CH3
    • •CH3 + Cl-Cl –> CH3-Cl + Cl•
  • Termination
    • Cl• + •Cl –> Cl-Cl
    • Cl• + •CH3 –> CH3-Cl
    • CH3• + CH3• –> CH3-CH3
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25
Q

(Alkane Reactions)

Substitution Reactions

Methane + Br2

A
  • Br2 undergoes homolytic fission
  • 1 Br molecule joines with an H molecule which breaks away from CH4

CH4 + Br2 –(UV)–> CH3Br + HBr

26
Q

(Alkene Reactions)

Chemical Properties

A
  • sp2 hybridized at 120 degrees with an outer π bond that is the site of reactivity allowing range of addition reactions
  • bonds in C=C are not as stable as single bonds –> energetically favorable to be converted to single bonds
    • they have a high electron density making their activation energy low
27
Q

Addition Reactions

A
  • HX + Alkene –> Halogenoalkane
  • Halogen + Alkene –> Halogenoalkane
  • Water + Alkene –> Alcohol
  • Polymerization
28
Q

Summary of Alkene Reactions

A
29
Q

(Alcohol Reactions)

Complete Combustion

A

C2H5OH(l) + 3O2(g) –> 2CO2(g) + 3H2O(l)

  • Extreme form of oxidation
  • Produces CO2 + H2O
  • Burns more cleanly than their equivalent alkanes
    • O in the compound is available for combustion products so less CO made in limited O2 conditions
      • Alcohols with longer chains have greater molar enthalpies, but may not be able to burn cleanly
  • Energy released increases down functional group
30
Q

Oxidation of Alcohols

(Tertiary vs Secondary vs Primary)

A

Tertiary Alcohol

  • C4OH –> not easily oxidized (resistant to normal oxidation)

Secondary Alcohol

  • C3HOH –> ketone C3O –> no further oxidation

Primary Alcohol

  • C2H2OH –> aldehyde C2OH –> carboxylic acid C2OOH
31
Q

Oxidation of Primary Alcohols

A
  • Alcohol is dripped into a warm solution of acidified KMnO4 / K2Cr2O7
  • K2Cr2O7 is reduced from orange to green
    • Cr(IV) –> Cr(III)
  • Aldehydes have low boiling points (no H bonding) ==> distill before being oxidized further
  • Reflux the mixture to produce acid
    • condense back into mixture from aldehyde ==> oxidized to acid
32
Q

Oxidation of Secondary Alcohols

A

CH3CHOHCH3 + [O] –> CH3COCH3 + H2O

propan-2-ol KMnO4 / K2Cr2O7 Propanone

  • Alcohol is refluxed with acidified K2Cr2O7 –> ketone
    • on prolonged treatment with a powerful oxidizing agent they can be further oxidised to a mixture of acids with fewer C atoms than the original alcohol
33
Q

Condensation - Esterification

A

Carboxylic Acid + Alcohol <—> Ester + Water

34
Q

Nucleophile

A

Reactants with a non-binding pair of electrons that are attracted to a positive carbon (a form of electrophile)

35
Q

Halogenoalkane Substitution Reactions

A
  • Halogenoalkanes are reactive and undergo nucleophilic substitution reactions from nucleophile attack

R-X(l) + OH-(aq) –> R-OH(aq) + X-(aq)

with NaOH:

CH3CH(Cl)CH2CH3 + NaOH –> CH3CH=CHCH3 + NaCl + H2O

conditions: heat (boil)

36
Q

Benzene Reactions: Electrophilic Substitutions

A

Nitration of Benzene

  • Firstly sulfuric acid is stronger so it protonates the nitric acid
  • with heat the electrophilic substitution by the nitronium ion causes a momentary loss of symmetry of the electron structure of benzene
37
Q

Reduction of Carbonyl Compounds

A
  • The oxidation of alcohols can be reversed by reduction

CH3COOH –[H+]–> 3CH3CHO –[H+]–> CH3CH2OH

carboxylic acid aldehyde primary alcohol

  • Needs lithium aluminium hydride LiAlH4 in dry ether

(CH3)2CO –[H+]–> (CH3)2CHOH

Ketone Secondary Alcohol

  • Needs heat with sodium borohydride NaBH4
38
Q

Reduction of Nitrobenzene

A
39
Q

Synthetic Route

A

A series of discrete chemical steps to change a reactant to a desired product

40
Q

Configurational vs Conformational Isomerism

A

Configurational

  • can be interconverted only by breaking bonds

Conformational

  • can be interconverted by free roation about σ bonds
41
Q

cis - trans Isomers

A
  • Cis isomers are those with the same groups on the same side of the double bond or cyclical compounds
  • Trans isomers have the groups on the opposite sides of the double bond
42
Q

E / Z Isomers

A
  • Isomers with more than 2 different groups, the group with the highest priority on the left hand side is determined, and then that of the right
    • E Isomers - have these two groups opposite
    • Z Isomers - have these two groups on the same side
  • Priority rules
    • the atom w/ highest atomic number
    • if atom the same, apply rule to next bonded atom in chain
43
Q

Properties of Isomers

A

Cis

  • Inductive effect leads to polarity –> higher b.p.
  • Limited/reduced intermolecular bonding –> lower b.p.

Trans

  • Inductive effects balance –> lower b.p.
  • Extensive intermolecular bonding –> higher b.p.
44
Q

Chiral Carbons

A
  • non-superimposable on each other
  • exists in pairs - enantiomers
  • diastereomers contain two or more chiral carbons –> not mirror images
45
Q

Optical Isomers Activity

A
  • Isomers differ in their reaction to plane-polarised light
  • plane polarised light vibrates in one direction only
  • one isomer rotates light to the right, the other to the left
    • reotation measured by polarimeter
  • if light appeares to have
    • turned to the right –> Dextrorotatory (d / +)
    • turned to the left –> Laevorotatory (l / -)
46
Q

Racemate / Racemic Mixture

A

A 50-50 mixture of the two enantiomers (dl) or (+-)

  • the opposite optical effects of each isomer cancel each other out
47
Q

Polarimeter

A
  • Light source produces light vibrating in all directions
  • polarising filter only allows through light vibrating in one direction
  • plane polarised light passes through sample
  • if substance is optically active it rotates the plane polarised light
  • analysing filter is turned so that light reaches a maximum
  • direction of rotation is measured coming towards the observer
48
Q

Racemic Mixture other facts

A
  • Formation of racemic mixtures is more likely in a lab reaction than in a chemical process occuring naturally in the body
  • if a compound can exist in one form, only one of the optical isomers is usually effective
  • the separation of isomers will make manufacturing more expensive
  • a drug made up of both isomers will require a larger dose –> may cause problems if the other isomer is ‘poisonous’ - a tetratogen
49
Q

Polar vs Non-polar Solvents

A

Polar

  • Have dipole moments due to different electronegativities (solvents must be polar or won’t react with H2O)

Non-polar

  • Similar electronegativities
50
Q

Protic vs Aprotic Solvents

A

Protic

  • Polar solvents with OH/ NH bonds allowing hydrogen bonding and a source of protons (eg water/ ethanol)

Aprotic

  • A polar / non-polar solvent that do not have OH/ NH bonds nor provide a source of protons (eg acetone, benzene, hexane)
51
Q

Electrophilic Addition Reaction - Ethene and Bromine

A
52
Q

Electrophilic Addition Reaction - Ethene and HBr

A
53
Q

Asymmetric Alkenes (Markovnikov’s rule)

A

The hydrogren will attach to the carbon that is already bonded to the greater number of hydrogens

54
Q

Propene and HBr

A
55
Q

SN2 Reaction Mechanism

A
  • Involve heterolytic fission + nucleophilic substituion with primary haolgenoalkane
  • unstable transition state created –> bimolecular
  • Rate = k[halogenoalkane][nucleophile]
  • Polar Aprotic Solvents preferred - unable to form H bonds (or solvent would bind to nucleophile inhibiting its action)
56
Q

SN1 Reaction Mechanism

A
  • Involve heterolytic fission + nucleophile substitution with tertiary halogenoalkane
  • Steric hindrance - halogen must be heterolytically removed to create a carbocation before nucleophile can be attached
    • creates more stable intermediate –> reaction is unimolecular
  • Polar protic solvents preferred -form H bonds which stabilize the carbocation by ion-diple interactions
57
Q

Positive Induction

A
  • Stabilization of a carbocation because the other alkyl groups can unevenly share their electrons with the positive centered carbon
58
Q

Enthalpy Level Diagram: SN1

A

Carbocation intermediate

59
Q

Enthalpy Level Diagram: SN2

A

Unstable transition state

60
Q

SN2 / SN1 Reaction mechanism

Effect of Leaving Group

A
  • As halogen-carbon bonds become less polar, it would be expected that the nucleophilic attack to be less and so rate decreases down the group
    • F > Cl > Br > I
  • In reality: energy to break bonds must be considered
    • C-I > C-Br > C-Cl > C-F
61
Q

SN2 / SN1 Reaction mechanism

Effect of Mechanism

A
  • In general SN1 tertiary reaction rates are faster than SN2 primary due to the stability of the formation of carbocations

Tertiary > Secondary > Primary

SN1 SN1 & SN2 SN2

IB Chemistry HL (19 decks)

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