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Core Chemistry 1A - Paper 1 > Organic > Flashcards

Organic Flashcards

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1
Q

3 rules for resonance structures

A

Must have same molecular formula
Must have same total number of electrons
Must have same atoms bonded together

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2
Q

3 legal moves of resonance

A

π bond -> lone pair
lone pair -> π bond
π bond –> π bond

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3
Q

What are constitutional isomers?

A

Isomers with different connectives

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4
Q

What are meta, para and ortho structures?

A

Apply to a benzene ring with 2 groups attached
meta - groups are 2 carbons away
para - groups are on opposite sides
ortho - groups are next to each other

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5
Q

What are conformational isomers?

A

Can be converted into each other by rotation around a single bond
eg anti and syn structures

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6
Q

What are enantiomers?

A

Non-superimposable mirror images of each other

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7
Q

What are diastereoisomers?

A

Non-superimposable, not mirror images of each other

eg E/Z isomers, chiral molecules

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8
Q

What are configurational isomers?

A

Involves the breaking of bonds to convert between the 2

2 types: diastereoisomers, enantiomers

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9
Q

What are the 2 types of stereoisomers?

A

Configurational

Conformational

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10
Q

What is a conjugated system?

A

Has 2 or more C=C bonds alternating with C-C bonds

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11
Q

More conjugation leads to…

A

Smaller HOMO-LUMO gap

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12
Q

For a reaction to take place, molecules must:

A

Overcome their electronic repulsion by charge attraction and/or orbital overlap

Have orbitals of appropriate energy to react - a filled orbital on the nucleophile and an empty orbital on the electrophile

Approach each other such that these orbitals can overlap to form a bonding interaction

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13
Q

Nucleophiles typically…

A

Have a non-bonding lone pair of electrons (high energy HOMO)
eg ammonia, amines, water,

Generally, the higher the pKa of AH, the better A- is as a nucleophile

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14
Q

Nucleophiles donate electrons from…

A 
Available, high-energy orbitals from:
a lone pair
a negative charge
a double bond
a σ bond to an electropositive atom
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15
Q

Electrophiles are…

A

Neutral or positively charged species with an empty atomic orbital or a low-energy antibonding orbital that can easily accept electrons

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16
Q

What makes a good electrophile?

A

Has a low-energy anti bonding orbital associated with an electronegative atom
e.g. Having a double or single bond to an electronegative atom

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17
Q

Electrophiles accept atoms into…

A

Empty low-energy orbitals represented by:
a positive charge representing an empty orbital
a neutral molecule with an empty p orbital
a double bond to an electronegative element
a single bond to an electronegative atom

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18
Q

What makes a stable anion?

A

Having the negative charge on an electronegative atom or by spreading the negative charge over several atoms

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19
Q

SN1 reaction

A
  • Unimolecular
  • Good LG needed
  • Must be able to form a stable carbocation intermediate
  • Nu independent
  • Polar and protic solvent to stabilise ions
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20
Q

SN2 reaction

A
  • Biomolecular
  • Good LG needed
  • Sterically unhindered substrates
  • Good Nu needed
  • Solvent: not protic, but polar to dissolve Nu
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21
Q

What molecules undergo an SN2 reaction?

A

CH3X > primary > secondary > tertiary (doesn’t react)

22
Q

What molecules undergo an SN1 reaction?

A

tertiary > secondary > primary (doesn’t react) > CH3+ (doesn’t react)

23
Q

What does the strength of an acid depend on?

A

The stability of the conjugate base

- the more stable the conjugate base, the stronger the acid

24
Q

What makes a good LG?

A

Weak bases - lower pKa means a better leaving group

25
Q

3 ways of making esters from alcohols

A
  • acid anhydride + pyridine
  • acid chloride + pyridine
  • carboxylic acid + acid catalyst e.g. HCl
26
Q

Order of reactivity of carbonyls

A

Acid chloride > Aldehyde > Ketone > Ester > Amide

27
Q

The R/S isomer has the groups in order of decreasing priority in which direction?

A

R clockwise

S anticlockwise

28
Q

Stereochemistry of SN1 and SN2 reaction

A

SN1 usually produces a racemic mixture

SN2 inverts the carbon being attacked

29
Q

What are hard nucleophiles?

A

Small, charged, basic, low-energy HOMO, like to attack C=O, e.g. RO-, NH2-, MeLi

30
Q

What are soft nucleophiles?

A

Large, neutral, not basic, high-energy HOMO, like to attack saturated carbon, e.g. RS-, I-, R3P

31
Q

Which structure is more stable, staggered or eclipsed?

A

Staggered

32
Q

What conditions favour elimination over substitution?

A

High temperatures

Nucleophiles that are strong bases and bulky

33
Q

What conditions favour E2 reaction over E1?

A

High base concentration and strong bases favour E2

34
Q

E1 reaction must…

A

Must form stable carbocation

35
Q

Regio and stereo selectivity of E1 reaction

A

E isomers are favoured over Z

More stable alkenes are favoured

36
Q

Regio and stereo selectivity of E2 reaction

A

E2 reactions favour more stable alkenes, but become more regioselective for the less substituted alkene with more hindered bases

37
Q

What can never be a leaving group for E2?

A

OH-

38
Q

Order of steps for E1, E2, E1cB

A

E1 - leaving group first, then deprotonation
E2 - deprotonation and leaving group simultaneous
E1cB - deprotonation first, then leaving group

39
Q

Reducing agents

A

NaBH4 - will only reduce aldehydes and ketones

LiAlH4 - will reduce all carbonyls

40
Q

Reagents for making an aldehyde from an alcohol

A

CrO3 (can over oxidise)
or PCC and DCM
or DMSO, (COCl)2, Et3N and DCM

41
Q

Enolate systems tautomorise between…

A

Enol (alkene alcohol) and ketone

42
Q

Markovnikov’s rule

A

For addition of HX across a double bond, the hydrogen will attach to the carbon with the most hydrogens on already

43
Q

Stereochemistry of adding Br2 to an alkene

A

Only anti product is formed (Brs on opposite sides)

Brs sticking up either side, with R groups dashed and wedged

44
Q

Stereochemistry for adding H2 to an alkene

A

Only syn product is formed (Hs on same side)

45
Q

Stereochemistry of adding HBr to an alkene

A

An equal mixture of anti and syn products are formed

46
Q

Alcohol + ketone –>

A

Acetal

where C=O was, turns into O-R (alcohol is ROH) going out both sides

47
Q

Ketone + amine –>

A

Imine

C=O goes to C=NR (amine is RNH2)

48
Q

Explain uses of enolates in organic chemistry

A
  • Explain what they are
  • Relative reactivity / stability
  • How to make them
  • Alkylations
  • Condensations (aldol and claisen)
  • Michael reactions
49
Q

Rough pKa of carbonyls

A 
Carboxylic acid - 5
Nitro - 9
Amide - 15
Alcohol - 17
Aldehyde - 17
Ketone - 20
Ester - 25
Nitrile - 25
Amine - 30
Alkane - 50
50
Q

Definition of a chiral molecule

A

Is not superimposable on its mirror image (lack of plane of symmetry or centre of symmetry)

51
Q

How to separate a mixture of entiomers

A

React with another chiral molecule to form diastereoisomers, which have different physical properties e.g. boiling point

Core Chemistry 1A - Paper 1 (2 decks)

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