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10. Organic Chemistry Flashcards

1
Q

What is organic chemistry?

A

Organic chemistry is the study of organic compounds, which are most compounds which contains carbon.

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2
Q

Describe the features of a homologous series

A
  1. Successive Δ-CH2group
  2. General formula & Functional group
  3. Gradation of physical properties
  4. Similar chemical properties (F.G.)
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3
Q

Predict and explain the trends in boiling points of members of a homologous series

A

^ Cn = ^ b.p.

^ Cn = ^ temporary dipole = ^ van der Waals’ forces

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4
Q

Distinguish between empirical, molecular and structural formulas

A

Empirical: Simplest whole number ratio

Molecular: Actual number

Structural: Bonding

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5
Q

What are structural isomers?

A

Structural isomers are compounds with the same molecular formula but with different arrangements of atoms

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6
Q

Draw primary, secondary and tertiary carbon atoms in alcohols and halogenoalkanes

A
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7
Q

Discuss the volatility of compounds containing the functional groups of alcohol, aldehyde, ketone, carboxylic acid and halide

A

Volatility = Δ => Gas, + Volatility = - boiling point = - IMF

Volalility depends on the legnth of hydrocarbon skeleton (+ Mr = - volatility, - branching = - volatiity) and the functional group => dipole-dipole / H-bonding

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8
Q

Discuss the solubility in water of compounds containing the functional groups of alcohol, aldehyde, ketone, carboxylic acid and halide

A

Solubility in water depends on the hydrocarbon skeleton the functional group:

Non-polar compounds are insoluble,

therefore + Mr = -Solubility

Functinoal group with hydrogen bonding are soluble,

therefore

V.soluble = Alcohol, C.Acid, Amines

Soluble = Aldehydes, Ketones, Amides, Esters

Not Soluble = Alkanes, Alkenes, Halogeno-alkanes

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9
Q

What are the classes of organic compounds and what is the difference between them?

A

There are 3 classes of organic compounds; primary, secondary and tertiary. A primary carbon atom is bonded to the functional group and two hydrogen atoms, a secondary carbon atom is bonded to the functional group, one hydrogen atom and 2 alkyl groups, and a tertiary carbon atom is bonded to the functional group and three alkyl groups.

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10
Q

What are esters?

A

Esters are alcohols with an alkyl group replaced by a hydrogen atom from a carboxylic acid.

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11
Q

How are esters named?

A

Esters are named according to their alkyl group followed by their acid anion. Name: [Alkyl group][Acide Anion] Ex. C2H5COOH3 = methyl propanoate

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12
Q

What are amides?

A

Amides are acid derivatives with the -OH group replaced by a N- group.

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13
Q

What are the 3 groups of amide, and how are they named?

A

There are primary, secondary, and tertiary amides. Primary amides only have an -NH2 group, while secondary and tertiary amides have 1 and 2 alkyl group attached to the nitrogen respectively.

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14
Q

What are the stems of the name of carbon chains from C1 to C6?

A
  1. Meth- 2. Eth- 3. Prop- 4. But- 5. Pent- 6. Hex-
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15
Q

What are the main homologous series, their functional group, and their suffixes?

A
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16
Q

What are the 3 rules of nomenclature in the IUPAC system?

A
  1. Identify longest straight chain C = stem
  2. Identify functinoal group = suffix
  3. Identify side chains / substituent group = prefix
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17
Q

What are structural isomers?

A

Structural isomers are compounds with the same molecular formula but with different arrangements of atoms.

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18
Q

What functional group is present in this molecule?

A

Amino (NH2)

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19
Q

What functional group is present in these molecules?

A

Benzene Ring (C6H6)

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20
Q

What functional group is present in this molecule?

A

Ester (RCOOR’)

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21
Q

What is the general formula of alkanes?

A

CnH2n+2

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22
Q

Why are alkanes unreactive?

A
  1. Strong bonds (High bond enthalpy)
  2. Non-polar
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23
Q

What is the chemical equation for the complete and incomplete combustion of alkanes?

A
  1. Alkane + excess O2 -> CO2 + H2O
  2. Alkane + limited O2 -> CO +H2O
  3. Alkane + extreme limited O2 -> C + H2O
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24
Q

What type of reaction do alkanes normally undergo in halogenation?

A

Substitution reaction

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25
What is the reaction of methane and ethane with chlorine and bromine?
1. CH4 + Cl/Br -\> CH3Cl / CH3Br 2. CH3CH3 + Cl / Br -\> CH3CH2Cl / CH3CH2Br Halogen replaces hyrdogen
26
How do halogenation occur with alkanes?
Through a free-radical mechanism
27
What are the stages of a free-radical mechanism for the halgenation of alkanes? Use the reaction of methane and ethane with chlorine and bromine as an example.
1. Initiation Cl2 (uv) -\> 2Cl• (Homolytic fission = break covalent bond, free radical with unparied electron) 2. Propagation Use & Produce free radicals -\> Continue reaction =\> Chain reaction e.g. Cl + CH4 -\> CH3• + HCl CH3• + Cl2 -\> CH3Cl + Cl• CH3Cl + Cl• -\> CH2Cl• + HCl CH2Cl + Cl2 -\> CH2Cl2 + Cl• 3. Termination Removal of free radicals e.g. Cl• + Cl• -\> Cl2 CH3 + Cl• -\> CH3Cl CH3• + CH3• -\> C2H6
28
What does a normal substitution often produce as a result of free-radical mechanism?
A mixture of different degrees of substitution
29
How do we ensure that there is a high yield of mono-chlorinated products in substitution reaction of methane and chlorine?
Use excess methane.
30
What is the symbol of a radical? Use Cl as an example.
Cl•
31
What is the general formula of alkenes?
CnH2n
32
Most reactions with alkenes are _____ reactions.
additonal
33
What is the chemical reaction for the hydrogenation of alkenes and what are the conditions required?
Alkene + Hydrogen -\> Alkane e.g. C2H4(g) + H2(g) -\> C2H6 Conditions: 1) 180C 2) Nickel catalyst
34
What are the different types of structural isomers? How do they differ?
The 3 types of structural isomers are 1) Chain - Carbon skeleton differs, 2) Position - Functional group location differs and 3) Functional group isomers - Different functional group
35
What is the economic importance of the reaction of alkenes?
1) Hydrogenation to convert vegetable/cooking oil to margarine, 2) Hydration to turn ethene into ethanol and 3) Polymerisation to make plastics, such as PVC and polystyrene.
36
Describe, using chemical equations, the halogenation of alkenes.
Alkene + Halogen -\> Di-haloalkane
37
Describe, using chemical equations, the reaction of alkenes with hydrogen halides (symmetrical).
Alkene + Hydrogen halide(g) -\> Haloalkane
38
What is the reactivity order of hydrogen halides?
HI \> HBr \> HCl (Strength decreases as length increases)
39
What is the chemical equation for the hydration of alkenes? And what are the conditions required?
Alkene + water(steam) -\> Ethanol Conditions required: 1) H3PO4 or H2SO4 catalyst, 2) 300C(high temperature) and 60atm
40
Describe, using chemical equations, the hydration of alkenes in 2 steps, with an example.
41
How do we distinguish alkanes from alkenes?
Bromine water test, alkenes react and decolourises bromine water, ie. red-brown -\> colourless
42
What is the chemical equation for the polymerisation of alkenes? Use 1) Poly(ethene), 2) Poly(chloroethene) and 3) Poly(propane) as examples.
Monomer --polymerisation--\> Polymer ex. Ethene -\> Polyethene, Chloroethene (vinyl chloride) -\> Polychroethene (PVC) Propene -\> Polypropene
43
What is the chemical equation for the complete combustion of alcohol?
Alcohol + Oxygen -\> Carbon dioxide + Water (Increase CO2 =\> Increase energy release)
44
Which is better as a fuel; alcohol or alkane? Why?
Alkane \> Alcohol because alcohol is in a more reduced state, e.g. Petrol \> Ethanol (but ethanol is renewable; fermentation)
45
What does the product of oxidation of alcohol depend on?
The product of the oxidation of alcohol depends on its nature: Primary/Secondary/Tertiary.
46
Using equations, describe the 2 stages of the oxidation of primary alcohols. What is oxidation in the 2 contexts? What is the oxidation agent?
Stages: 1) Alcohol + [O] -\> Aldehyde (RCHO) (Partial) and 2) Aldehyde + [O] -\> Carboxylic acid(RCOOH) (Full). Oxidation is the removal of H2 in stage 1 and is the addition of oxygen in stage 2. The oxidation agent is acidified potassium dichromate (VI) K2Cr2O7.
47
How do we control the oxidation of alcohol so that the aldehyde is formed instead of the carboxylic acid or vice versa?
**If the aldehyde is the desired product:** Heat reaction mixture in excess alcohol with distillation apparatus (to distill off aldehyde as it’s being formed) **If the carboxylic acid is the desired product:** Heat reaction mixture under reflux for a longer period of time with excess oxidizing agent (a vertical condenser to ensure the aldehyde drops back into reaction vessel for further oxidation to the carboxylic acid)
48
What is the difference between the apparatus in distillation and reflex?
Refluxing is a continuous process where the condensate runs back down to the reaction vessel, where as, distillation is a means to separate two substances based on their boiling point differences. Refluxing the reactants allows you to heat the reactants to the boiling point, condense the vapors that are produced, and return them to the reaction vessel. This is useful for many organic reactions which are slow and/or have low yields.
49
Using equations, describe the oxidation of secondary alcohol. Use propan-2-ol as an example.
Alcohol + [O] -\> Ketone. e.g. Propan-2-ol (CH3CH2OH) + [O] -\> Propanone (CH3COCH3)
50
What is the product of the oxidation of tertiary alcohol?
(Trick question). No product since no hydrogen is attached to hydroxyl carbon, it will occur only if carbon skeleton is broken.
51
What are the tests for distinguishing between aldehyde and ketones? What are the changes? Explain the changes.
1) Fehling's solution / Benedict's solution: Add solution, warm gently, Ketone: No change in blue solution, Aldehyde: Blue solution produces dark red precipitate of copper(I) oxide 2) Tollen's Reagent (Diamminesilver(I)ion = [Ag(NH3)2]+) : Add solution, Ketone: No change in colourless solution, Aldehyde: Colourless solution produces grey precipitate of silver, silver mirror on test on tube. 3) Potassium dichromate (VI) solution (Kr2Cr2O7): Add solution, Ketone: no change in orange solution, Aldehyde: Orange solution turns green.
52
What happens in the substitution reaction of halogenoalkanes? Why is the C-X bond reactive?
In the substitution of halogenoalkanes the X is replaced by another group. The C-X bond is reactive due to polarity difference; X is more e-negative than C.
53
What are nucleophiles?
A species with lone pair of e- which can be donated to an e- deficient centre of an organic compound.
54
What are the 2 types of mechanism for nucleophilic substitution of halogenoalkanes?
The two types of mechanisms are Sn1 and Sn2, and is dependent upon the nature of the molecule (Primary, secondary or tertiary).
55
What are the predominant mechanisms for the nucleophilic subsitution of primary, secondary, and tertiary halogenoalkanes?
Primary : Sn2 Secondary : Sn1 & Sn2 Tertiary : Sn1
56
What are the chemical equations and processes for the nuclephilic substitution of CH3CH2Br with sodium hydroxide?
57
What are the chemical equations and processes for the nuclephilic substitution of CH3C(CH3)2Br with sodium hydroxide?
58
Draw the reaction pathway, with conditions and type of chemical reaction.
59
Why is the hydroxide ion a better nucleophile than water?
Because OH- have a formal negative charge and lone pair is readily available. On the other hand H2O does not have a formal negative charge and lone pair is not readily available.
60
What are nucleophiles?
Nucleophile are reagents that "seek out" regions of positive charge and have a lone pair of electrons to bond with postively charge or partially postively charge centers.
61
Explain how the rate of nucleophilic substitution in halogenoalkanes by the hydroxide ion depends on 1. The identitiy of the halogen 2. Whether the halogen is primary, secondary or tertiary
Both the elctronegativity and the size of the halogen affect the rate of nucleophilic substitution. More electronegative halogens will polarise the carbon atom more easily, increasing rate of reaction. However larger halogens have weaker bonds which break more easily, and the size factor wins over the electronegativity factor. Therefore rate increases as size of halogen increases. ie. Rate: I \> Br Sn1 mechanism is faster than Sn2 as there is only 1 rate determing factor; the reaction is unimolecular. Therefore Rate: Tertiary \> Secondary \> Primary
62
Write the equation for the substitution reaction of halogenoalkanes (bromoethane) with 1. Ammonia 2. Potassium Cyanide
Ammonia : NH3 + CH3CH2Br =\> CH3CH2NH2 +HBr Cyanide : KCN + CH3CH2Br =\> CH3CH2CN + KBr
63
What is the problem of using ammonia to produce primary amine? How do we ensure a better yield?
The problem is that the primary amine formed still has lone pair on N and this is made more available by the positive induction effect of the alkyl group, it will further reack adn form amine salt mixtures, ie. CH3CH2N2 + CH3CH2Br =\> (CH3CH2)NH + HBr Higher yield is achieved by using excess ammonia (increase probablity of reaction with ammonia other than other products)
64
Why is the cyanide ion a good nucleophile?
Because it has a formal negative charhe and a readily available lone pair of electrons on the carbon atom
65
What is the advantage of suing cyanide ion in nucleophilic substitution reactions?
It adds a carbon atom to the chain
66
What can be converted from the resultant nitrile produced in nucleophilic substitution of cyanide? How?
1. Nitrile can be hydrolysed into carboxylic acid by heating with dilute acid CH3CH2CN + 2H2O + H+ =\> CH3CH2COOH + NH4+ 2. Nitrile can be transformed to amine by heating with hydrogen at 150C with nickel catalyst CH3CH2CN + 2H2 =\> CH3CH2CH2NH2
67
Draw and explain the SN2 mechanism of primary halogenoalkanes with 1. Ammonia 2. Potassium Cyanide
68
What is the chemical reaction for the reduction of nitrile? (butanenitrile with hydrogen) What are the conditions required?
CH3CH2CN + 2H2 =\> CH3CH2CH2NH2 150C Nickel catalyst
69
What happens in elimination reactions?
Elimination reactio is the removal of a small molecule from a large molecule, which is the reverse of addition reactions.
70
Write the chiemical equation for the elimination fo HBr from bromoalkanes. (Use 1-bromopropane as example) What are the conditions required?
CH3CH2CH2Br + NaOH =\> CH3CHCH2 + NaBr + H2O 1. Hot OH solution of a base 2. Alcohol solvent
71
Draw the mechanism for the elimination of HBr from bromoalkanes. (Use 1-bromopropane as example) (Both E1 and E2, and which is favoured?)
E2 is favoured
72
What happens in condensation reactions?
Condensation reaction is the addition of two molecules, forming a larger product and a by-product. Therefore it is also refered to as addition-elimination reactions.
73
Write the chemical reaction fo alcohols with carboxylic acids. Choose your own example. Name the reactants and products.
ex. CH2CH2OH + CH3COOH \<=\> CH3COOCH2CH3 + H2O Name: [Alkyl of alcohol][Acid Salt] ex. methanol + ethanoic acid \<=\> methyl ethanoate
74
What are the uses of esters?
1. Food flavouring 2. Perfumes 3. Plasticizers (soften plastic to increase plasticity) 4. Naturally occuring fats/oils (triglycerides)
75
Write the chemical equation for the reaction of amines with carboxylic acid. Choose your own example.
CH3COOH + CH3NH2 =\> CH3CONH(CH3) + H2O
76
What is formed when primary amine and secondary amine react with carboxylic acids?
Secondary and tertiary amines.
77
Draw "block diagrams" for the formation fo condesation polymers of esters and amines.
78
Outline the economic importance of condensation reactions.
Synthetic polyamines : Nylon 1. Clothing 2. Carpets 3. Tyre cords 4. Ropes 5. Machine parts (And the uses of esters)
79
What are stereoisomers?
Stereoisomers are compounds with the same structural formula but with different arrangement of atoms in space.
80
What are the types of stereisomerism?
Geometric and optical
81
Using 1,2-dibromoethane as an example, draw and name its geometric isomers.
82
Describe and explain the difference in physical properties of geometric isomers.
Example: 1,2-dibchloroethane. Since both Cl is on the same side in the CIS isomer, and the C-Cl bond is polar, the molecule is polar overall. In the TRAS isomer the two polar regions cancel out. Therefore b.p. CIS \> TRANS Example: Butanedioic acid The two COOH group are close in CIS, so there is more intramolecular H bond and less intermolecular H bond This does not occur in TRANS Therefore m.p. TRANS \> CIS
83
Describe and explain the difference in chemical properties of geometric isomers
Example: but-2-ene-1,4,-dioic acid In CIS the two COOH groups are close and therefore they condense on heating, forming cyclic anlydride (Butenoic Anhydride) and eliminating water. The two COOH groups are too far apart in TRANS for this to happen.
84
Draw geometric isomers in cyclic structures. Use dicholoro-cyclopropane and dicholoro-cyclobutane as examples
85
What are optical isomers?
Optical isomers are molecules which have non-superimposible mirror images
86
What are the names for a carbon atom joined to 4 different atoms or groups?
Asymmetric or chiral
87
What are enantiomers?
Molecules which have non-superimposible mirror images.
88
What is a racemic mixture?
A mixture with equimolar of 2 optical isomers, therefore the rotation effect on polarized light cancles out. ## Footnote This is also known as external compensation
89
Draw the optical isomers of butan-2-ol and 2-bromobutane
90
Define "Plane-polarized light"
Light in which all light waves vibrate in the same orientation.
91
How does a polarimeter distinguish optical isomers?
1. Light passes through a polarizing filter 2. Plane Polarized light passes through solution 3. To the analyzing filter. Information such as the type of enantiomer is determined by the angle of rotation. Enantiomers causes angle to rotate at opposite angles Other information includes path legnth and concentration of enantiomer
92
What are the differences in physical and chemical properties of enantiomers?
**Physical ** Identical excpet how they cause plane polarized light to rotate (and the formation of crystals) **Chemical ** Identical except when reacting with other optically active molecules

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