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Chemistry > Organic Chemistry Pt 1 - Week 7-9 > Flashcards

Organic Chemistry Pt 1 - Week 7-9 Flashcards

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1
Q

Molecular formula defintion:

A

Type and number of each element present

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2
Q

What 4 things must be specified when naming organic molecules?

A
  • Carbon chain length
  • Functional group class
  • Any substituents present and where they are
    on the molecule
  • Put everything together in alphabetical order
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3
Q

What is the priority order for functional groups?

A

Carboxylic acid — top priority
Ester
Acyl halide
Amide
Nitrile
Aldehyde
Ketone
Alcohol
Thiol
Amine
Ether
Alkene
Alkyne
Alkyl halide

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4
Q

Draw out 4-bromo-5-hydroxy-6-methylhepta-2-one

A

Longest chain is 7 –> hepta-
Principal group is C=O –> one ending
OH –> hydroxy
Br –> bromo
CH3 –> methyl

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5
Q

What are the 4 key physical properties of hydrocarbons?

A

States of matter: C1 - C4 gasses
C5 - C17 liquids
C17+ solids

Less dense than water

Molar mass increases with chain length

Boiling point - increases with chain length
- decreases with branching

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6
Q

What 4 factors are affected by increasing chain length?

A
  • Increases bp
  • Increases strength of van der Waals forces
  • Increases Mr
  • More likely to be liquid or solid at RT
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7
Q

Which linear molecules can contort into different conformations?

A

Alkanes can contort into different conformations –> due to rotation of bonds

Alkenes are frozen in a particular conformation

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8
Q

What are the two possible conformations of cyclic molecules and how do conformations occur?

A
  • Chair
  • Boat

Conformations have an energy difference so a particular conformation dominates at rt.

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9
Q

What are constitutional isomers (structural isomers) ?

A
  • Chain isomers
  • Position isomers
  • Functional group isomers
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10
Q

How can you identify between geometric isomers?

A

Use E/Z or cis/trans system.

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11
Q

What are the 3 rules for assigning highest priority groups?

A

Higher atomic number = higher priority

If a group has to atoms of the same type bonded to the alkene follow the chain until a difference in priority occurs.

Bonds of a double bond are counted additively e.g. worth 2 single bonds same in an alkyne (‘worth’ 3 single bonds)

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12
Q

How does the E/Z system work?

A

Assign priority to each group on a C in the C=C

High priority on same side = Z
High priority on opposite side = E

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13
Q

How does the Cis/ trans system work?

A

Need each C to have one group in common

Same side = Cis
Opposite side = Trans

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14
Q

What occurs with the combustion of hydrocarbons?

A

Hydrocarbons combust to form carbon dioxide and water

Incomplete combustion forms carbon monoxide and water

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15
Q

What is a nucleophile?

A

electron donor, has an excess of electrons
Loves nuclei

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16
Q

What is an electrophile

A

Neutron donor, has and excess of neutrons
Loves electrons

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17
Q

What reaction do alkenes undergo?

A

React via electrophilic addition mechanism - due to nucleophilic C=C

Addition of X2 to form a dihaloalkane
Addition of H2 to form an alkane

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18
Q

What is markovnikov’s rule?

A

The major product forms from the addition of the (electrophile) H atom to the C with the most H atoms.

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19
Q

What conditions are required for the hydration of alkenes?

A

A small amount of concentrated acid as a catalyst - H3PO4 or H2SO4

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20
Q

What are the special characteristics of arenes?

A

Arenes have a special type of delocalisation that imparts special stability.

Alternating double and single bonds are conjugated with delocalised pi-electrons.

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21
Q

What are the 3 criteria for the Hukel criteria for aromaticity?

A
  1. The compound must be cyclic
  2. The atoms in the ring must be sp2
    hybridised (have a free p-orbital)
  3. The sum of the electrons contained in the p
    orbitals must correspond to 4n + 2
    electrons n= 0, 1, 2, 3 (2e-, 6e-, 10e-, 14e-)
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22
Q

What are haloalkanes?

A

Alkanes containing a halogen atom (F, Cl, Br, I)

Polar molecules have a permanent dipole at the carbon halogen bond

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23
Q

What are 3 haloalkanes that are commonly used as solvents?

A
  • 1,2- dichloroethane
  • dichloromethane (DCM)
  • Chloroform
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24
Q

What are 4 reasons why haloalkanes are commonly used as solvents?

A
  • have a moderate polarity compared to water
  • able to dissolve most organic compounds
  • Lower bp means easier to evaporate off
  • DCM and chloroform are non-flammable
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25
Q

What are the physical properties of halogenated alkanes? State, solubility, density, intermolecular forces and boiling point?

A

State - Usually liquid (or solid) at RT
(exceptions are CH3Cl and CH3Br)

Solubility - haloalkanes generally soluble with
organic solvent
- Haloalkanes insoluble in water

Density - More dense than water

Intermolecular forces - Dipole-Dipole, Van der
Waal

Boiling point - higher than hydrocarbons of
similar length
- type of halogen atom increases
as you go from Cl -> Br -> I
- number of halogen atoms

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26
Q

Why are halogens often used in drugs?

A
  • slow down metabolic processes of the drug
  • based on natural products
  • improve bioavailability
  • improve activity of drug relative to non-
    halogenated analogue
  • Decreases lipophilicity -> less drug gets lokes
    in fat stores
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27
Q

What is the difference between protic and aprotic solvents?

A

Polar protic solvents have a permanent dipole and can make H-bonds (usually have an O-H bond)
Polar protic solvents stabilise ions making them less reactive

Polar aprotic solvents have a permanent dipole but cannot make H- bonds
Ions are more reactive in polar aprotic solvents.

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28
Q

What are the two competing reaction pathways for haloalkanes?

A

Substitution pathway
Elimination pathway

29
Q

What is nucleophilic substitution?

A

The nucleophile substitutes for a good leaving group on the molecule.
- Accesses new functional group classes
- Uses a variety of nucleophiles

30
Q

What are the two types of nucleophilic substitution?

A

First order nucleophilic substitution (SN1)

Second order nucleophilic substitution (SN2)

31
Q

What 3 things makes something a good nucleophile?

A
  • Full negative charge
  • Electronegative atom
  • Small (not bulky)
32
Q

Name 3 good nucleophiles and 3 weak nucleophiles:

A

Good = O-H, R-O, H3C-O, X
Weak = H2O, R-OH, R-SH, NH3

33
Q

What makes something a weak nucleophile?

A

Has a free lone pair with a partial negative charge rather than a full negative charge.

34
Q

What are the key steps in the SN2 general mechanism?

A
  • Backside Nucleophile attack
  • intermediate forms
  • inversion of stereochemistry
35
Q

What are the steps in the SN1 mechanism?

A
  • Leaving group leaves
  • Intermediate forms
  • Nucleophilic attack
  • If chiral racemic mixture produced
36
Q

What pathway do methyl and primary haloalkanes always react via?

A

SN2 pathway

37
Q

What pathway do tertiary haloalkanes always react via?

A

a SN1 pathway

38
Q

What pathway do secondary haloalkanes react by?

A

a mixture of SN1 and SN2

39
Q

What solvent is best for SN1 pathways?

A

Polar protic solvents

40
Q

What solvents are best for SN2 pathways?

A

Polar aprotic solvents.

41
Q

Which pathways do good nucleophiles favour?

A

SN2 pathways

42
Q

Which pathway do weak nucleophiles favour?

A

SN1 pathway

43
Q

What do elimination reactions do to haloalkanes?

A

Convert haloalkanes into alkenes

Base attracts a beta H and leaving group leaves.

44
Q

What are the steps to an E2 general mechanism?

A

Base is attracted to a hydrogen atom.
Transition state formed
Beta hydrogen elimination kicks off leaving group

45
Q

What are the steps to an E1 general mechanism?

A

Leaving group leaves
Beta hydrogen elimination quenches positive carbon
Product forms + (Base + H group)

46
Q

What is the trend with alkene stability?

A

the more C groups bound to C=C the more stable it is

47
Q

Which out of E - alkenes and Z - alkenes are the most stable?

A

E-alkenes are more stable than Z-alkenes

48
Q

What is Zaitsev’s rule?

A

The major product formed will be the most stable alkene.

49
Q

What pathway do primary haloalkanes undergo?

A

E2 pathway only

50
Q

What pathway do secondary and tertiary haloalkanes undergo?

A

Either E1 or E2 pathway

51
Q

Which solvents are best for E1 pathway?

A

Polar protic solvents

52
Q

Which solvents are best for E2 pathway?

A

Polar aprotic solvents

53
Q

What bases are favoured for E2 pathway?

A

Strong bases (preferentially hindered bases)

54
Q

What bases are favoured for E1 pathway?

A

Weak bases

55
Q

What are sterioisomers?

A

Isomers with the same molecular and structure, just a different 3D arrangement of atoms.

Requires a molecule with at least one stereocentre

56
Q

What is an optical isomer?

A

Molecules with the same molecular and structural formula but are not superimposable.

  • Need at least one sp3 hybridised C atom
    bound to 4 different groups.
57
Q

How do you assign R/S configuration?

A

Rank the 4 groups 1 - highest, 4 - lowest. H is always 4, lowest priority.

Rotate the molecule so the lowest priority is in the back, draw a circle going 1 -> 2 -> 3

58
Q

What configuration does a clockwise molecule show?

A

R configuration

59
Q

What configuration does an anticlockwise molecule show?

A

S configuration

60
Q

How can you work out the maximum number of stereoisomers?

A

= 2^n n = number of stereocentres

61
Q

What are enantiomers?

A

a pair of molecules that are mirror images because all chiral carbons in the molecule have opposite configurations

62
Q

What are diastereomers?

A

Not mirror images

63
Q

What are the 2 factors necessary for a molecule to be chiral?

A
  • at least two chiral C’s
  • at least one chiral C where the configuration
    is not switched
64
Q

What is a racemic mixture?

A
  • a mixture containing equal amounts of both
    enantiomers
  • specific rotation is zero
65
Q

What are arenes?

A
  • Cyclic aromatic molecules
  • All atoms in the ring are sp2 hybridised
  • P- orbitals contain 4n + 2 electrons ( 2e-, 6e-,
    10 e-, 14 e-, … )
66
Q

What naming system is used for di - substituted benzene derivatives?

A

Ortho , Meta, Para

One More Place

67
Q

What are the 6 reaction mechanism that benzene can undergo?

A
  • Electrophilic aromatic substitution
  • Halogenation
  • Nitration
  • Sulfonation
  • Friedel - Crafts Acylation
  • Friedel - Crafts Alkylation
68
Q

What are the 3 key stages of electrophilic aromatic substitution?

A
  1. Activation of electrophile
  2. Nucleophilic attack and loss of aromaticity
  3. Deprotonation and restoration of
    aromaticity

mechanism preserves aromaticity and special stability it gives

Chemistry (10 decks)

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