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Core Chem 1A - Term 1 > Organic > Flashcards

Organic Flashcards

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1
Q

Structure of acetone

A
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2
Q

Structure of acetontrile

A
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3
Q

Structure of toluene

A
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4
Q

Tetrahydrofuran structure

A
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5
Q

Diethyl ether structure

A
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6
Q

Pyridine structure

A
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7
Q

Dimethylsulfoxide (DMSO) structure

A
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8
Q

N,N-dimethylformamide (DMF) structure

A
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9
Q

General structure of an acetal

A
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10
Q

General structure of a carbonate

A
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11
Q

General structure of a nitrile

A
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12
Q

General structure of an ancyl chloride

A
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13
Q

What is a conjugated system?

A

A system with two or more C=C bonds alternating with C-C bonds

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14
Q

Briefly describe an SN1 reaction

A
  • Substitution Nucleophillic Unimolecular
  • Reaction passes through a carbocation intermediate
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15
Q

HA + H2O <–> A- + H3O+

Ka =

A

[A-][H3O+] / [HA]

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16
Q

pKa =

A
  • log (Ka)
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17
Q

pKa range of strong acids

A

-10 to 0

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18
Q

pKa range of weak acids

A

0 to 16

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19
Q

pKa range of very weak acids

A

16 to 50

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20
Q

pH =

A

pKa + log ( [HA] / [A-] )

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21
Q

What is a constitutional isomer?

A

Same molecular formula, different connectives

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22
Q

What is a stereoisomer?

A

Same molecular formula, same connectives

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23
Q

What are the two types of stereoisomers?

A

Configurational - 2 types

Conformational - Molecules can be converted into one another by rotation around a single bond

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24
Q

What are the two types of configurational isomers?

A

Enantiomers - Non-superposable mirror images

Diastereoisomers - Non-superposable, not mirror images
eg. E/Z isomerism
‘One end stays the same, the other is mirrored (wedge and dash switch)’

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25
Q

What is a chiral molecule?

A

A molecule that has a non-superposable mirror image. Has none of the following symmetry elements: A mirror plane, a centre of inversion, a rotation-reflection axis

26
Q

What is an achiral molecule?

A

A molecule that has a superposable mirror image

27
Q

What is a prochiral molecule?

A

A molecule that can be made chiral by swapping/adding one group

28
Q

Measurement of optical activity formula

A

observed angle of rotation (o) / [path length (dm) x concentration (g ml-1)]

29
Q

How to decide if an isomer is E or Z

A

Find highest priority group on each carbon

  • Higher atomic number

2 highest priority groups are on the same side is the Z isomer, when they are on the same side it is the E isomer

30
Q

How can the configuration of 2 diastereoisomers (E/Z) be determined?

A
  • They will differ in boiling point and the C13 and H1 NMR spectrums will differ, but it is hard to assign the configuration this way
  • If crystals of either can be grown at low temperature, the crystal can be analysed by X-ray crystallography to determine the configuration
31
Q

How can the confoguration of 2 diastereoisomers (anti/syn) be determined?

A
  • They are difficult to distinguish or separate
  • Might be able to use low temperature microwave spectroscopy
32
Q

How to decide if an isomer is anti or syn

A

The syn isomer will have the 2 highest priority groups (or the 2 groups that have been added) on the same side, the anti isomer will have them on opposite sides

33
Q

What physical properties will 2 constitutional isomers differ in?

A

They will have different melting points, and their C13 and H1 NMR spectrums will differ (give examples)

34
Q

On benzene, where do the ortho, meta and para groups lie?

A
35
Q

How can the configuration of 2 enantiomers be determined?

A

They can be distinguished by their ability in solution to rotate the plane of plane-polarised light

The actual configuration can be determined by X-ray crystalography of a single crystal sample of a pure enantiomers

36
Q

More conjugation leads to…

A

Smaller HOMO-LUMO gap

ie absorbs lower energy

37
Q

Factors determining the strength of the acid

A
  • Most important: Stability of the conjugate base, a more stable conjugate base means a stronger acid
  • Bond strength H-A, the easier the bond is broken, stronger the acid
  • The solvent, the better the solvent is at stabilizing the ions formed, the stronger the acid
38
Q

What makes a more stable conjugate base?

A
  • If the negative charge is on a more electronegative atom, the conjugate base will be more stable
  • Delocalization of the negative charge, the more spread out the charge is, the more stable the conjugate base
39
Q

Explain which is more acidic: phenol or nitrophenol

A
  • The molecules both react with water, leaving a negative charge on the O
  • Nitrophenol has an NO2 group which is electron-withdrawing, stabilizing the conjugate base with inductive effects
  • So nitrophenol is more acidic
40
Q

Describe the structure of nitrophenol

A

HO - benzene - N+ = O
|
O-

41
Q

Briefly describe an SN1 reaction

A
  • Leaving group goes first
  • Carbocation is formed
  • Nucleophile attacks next
42
Q

Briefly describe an SN2 reaction

A

Nucleophile attacks at the same time as the leaving group goes

43
Q

The rate of an SN2 reaction depends on…

A

The concentration of the substrate and the concentration of the nucelophile

44
Q

What increases the strength of inductive effects?

A

More electronegative atoms on the molecule, and these atoms being closer to the ionisation site

45
Q

Small pKa =

A

a strong acid

46
Q

Explain how to draw R and S isomers

A

Rank the groups from highest to lowest priority

Place them as follows:

R - starting from the top bond, go clockwise (rectus) putting the lowest priority group at the back

S - starting from the wedge, go anticlockwise (sinister) putting the lowest priority group at the back

47
Q

What is topicity?

A

It relates atoms, groups or faces to each other within molecueles

48
Q

What does constitutionally heterotopic mean?

A
49
Q

What does homotopic mean?

A

Atoms, groups or faces are related by an n-fold rotation axis, and the molecules are essentially the same

Eg. Gives the same molecule when Hs are replaced in turn, so the H atoms are homotopic

50
Q

What does enantiotopic mean?

A

Constitutionally identcal atoms, groups or faces in molecules which are related by a mirror plane, inversion centre or improper rotation axis. Replacement of one pair of enantiotopic groups forms one of a pair of enantiomers

51
Q

What does diastereotopic mean?

A

Constiutionally equivalent atoms, groups or faces of a molecule which are not symmetry related. Replacement of one or two diastereotopic atoms or groups results in the formation of one of a pair of diastereoisomers

52
Q

The rate of an SN1 raction depends on…

A
  • The carbon skeleton
  • The leaving group
  • Temperature
  • Solvent
53
Q

What substrates are likely to undergo SN1 mechanism?

A

Tertiary (excellent)
- Nu’s attack is hindered and a carbocation is readily formed

Secondary (moderate)

Allylic (double bond) (good)

Benzylic (good)

Adj. lone pair

54
Q

What substrates are likely to undergo SN2 mechanism?

A

Methyl (good)
- Nu can attack unhindered and a carbocation forms reluctantly

Primary (good)

Secondary (moderate)

Allylic (double bond) (good)

Benzylic

α-carbonyl

55
Q

What makes a good leaving group?

A

A weak base / a strong acid

eg I, Cl

OH is never a leaving group (unless protonated with a string acid)

56
Q

What makes a good nucleophile?

A

Charge
- Nucleophillicity increases with charge density

Electronegativity
- Nucleophillicity is the donation of an electron pair, the less electronegative the atom, the less ‘tightly held’ the electrons will be, so the better nucleophile

Solvent
- In polar protic solvents, nucleophillicity increases going down the periodic table. The capacity for hydrogen bonding is highest at the top of the periodic table, less hydrogen bonding means the nucleophile is less hindered

Steric hinderance
- Less sterically hindered (less bulky) nucleophiles are better

57
Q

Examples of polar protic solvents

A

Acetone, DMF, MeCN, DMSO

58
Q

Why is OH- a good nucleophile?

A

It is a strong base

59
Q

Characteristics of a hard nucleophile

A
  • Small
  • Charged
  • Basic
  • Low-energy HOMO
  • Like to attack C=O
  • Such as RO-, NH2-, MeLi
60
Q

Characteristics of a soft nucleophile

A
  • Large
  • Neutral
  • Not basic
  • High-energy HOMO
  • Like to attack saturated carbon
  • Such as RS-, I-, R3P
61
Q

Why is tBu a bad electrophile?

A

Gives steric hinderance to the approach of the Nu, raising the energy of the transition state structure, giving a very slow rate of reaction

62
Q
A

Core Chem 1A - Term 1 (6 decks)

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