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Year 1 Chem > Organic > Flashcards

Organic Flashcards

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1
Q

How do you determine the functional group level of a molecule?

A

The number of bonds to a heteroatom from a given carbon atom, double bonds count as two and triple bonds count as 3

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2
Q

What functional group level is a carbon atom that is connected to an O by a double bond, an OH by a single bond, and a C by a single bond?

A

3, two bonds to O which is a heteroatom and one bond to O which is a heteroatom, therefore it is functional group level 3

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3
Q

Why are peroxides reactive?

A

It has a weak O-O bond that can be easily broken

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4
Q

What does a large functional group number mean in terms of oxidation?

A

The molecules with the largest functional group numbers are the most oxidised

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5
Q

What does a small functional group number mean in terms of oxidation?

A

The molecules with the smallest functional group numbers are the most highly reduced

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6
Q

When an alcohol reacts to form an aldehyde is this reduction or oxidation?

A

Oxidation, the alcohol loses one electron for each hydrogen that is lost

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7
Q

When an alkane is oxidised to form an alkene what happens to the functional group number?

A
  • The functional group number increases by 1
  • This means that an alkene is functional group number 1
  • Alkynes are functional group number 2
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8
Q

What is the I- inductive effect?

A
  • Groups that have an electron withdrawing effect have the I- inductive effect
  • Oxygen and the halogens have a I- effect as they are electronegative and attract electrons towards them in a bond
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9
Q

What is the I+ inductive effect?

A
  • Groups that have an electron donating effect have the I+ inductive effect
  • In a bond they push electrons towards the other atom
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10
Q

Does a methyl group have a + or - I effect?

A

I+, it pushes electrons towards the other atom in the bond

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11
Q

Which carbons are the most reactive?

A
  • Carbons with the biggest δ+ will be the most reactive as they attract nucleophiles the most
  • Carbons with the biggest δ- will be the most reactive as they have the biggest electronegativity, they will react with electrophiles
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12
Q

How does heterolytic fission work?

A
  • The electrons from the bond between two atoms move towards the more electronegative atom, this causes the bond to break, the electronegative atom is now negatively charged as it has gained an electron
  • The delta positive atom is now positively charged as it has lost an electron
  • The negatively charged atom’s Lewis structure can be drawn as having 6 electrons and a negative charge in a circle which represents 2 electrons
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13
Q

How does homolytic fission work?

A

The bond between two atoms breaks and one electron goes to each atom, 2 radicals are formed each with 7e-

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14
Q

What is the mesomeric (resonance) effect?

A

The movement of electrons within a molecule to move a charge from one atom to another, having multiple resonance forms makes a molecule more stable as the charge can be spread out

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15
Q

Why are tertiary carbocations more stable than secondary and primary carbocations?

A

The connected CH3 groups have a +I effect which means they donate electron density to the central carbon, this reduces the positive charge of the carbocation and makes it less reactive and therefore more stable

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16
Q

Does the +M or +I effect make a carbocation more stable?

A

+M effect has a greater effect on stability than the +I effect so carbocations that have resonance forms are more stable than carbocations connected to substituents with the +I effect

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17
Q

When a carbocation with fluorine connected to it forms a resonance form, is this more stable than a carbocation with oxygen connected?

A

It is less stable as when the resonance form is formed, the double bond between fluorine and carbon has the electron density lying closer to the fluorine than the oxygen in the C=O bond. This means that the carbocation is more positive when there is a C=F bond than when there is a C=O bond.

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18
Q

What is more stable carbocation out of CH3C+(F)CH3 and CH3C+(H)CH3?

A

Although CH3C+(F)CH3 has a resonance form, CH3C+(H)CH3 is more stable as the C=F bond in the resonance form doesn’t have as big of a +M effect as when resonance forms are formed with oxygen

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19
Q

What is the order of priority for the origin of electron flow?

A

Highest - Negative charge
- Lone pair
- Double bond
Lowest - Single bond

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20
Q

What is the order of priority for the flow of electron charge?

A

Highest - Positive charge on a carbon or H+
- Atom adjacent to charge on heteroatom
Lowest - Delta positive charge

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21
Q

What are the rules when drawing electron flow?

A
  • Electron flow must follow bonding rules

- Electron flow won’t cause a carbon atom to have 5 bonds

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22
Q

What are curly arrows a simplified illustration of?

A

Orbital overlap, when you draw a curly arrow from a nucleophile to an electrophile, the electrophile will have an empty p orbital and the nucleophile will have a full p-orbital, these overlap to form a single bond

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23
Q

What is the difference between a base and a nucleophile?

A

A base is a nucleophile that will only react with H+ or Hδ+

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24
Q

What is the difference between an acid and an electrophile?

A

An acid is an electrophile that will only react with a base

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25
Q

When an acid reacts with a base which orbital reacts with which?

A

The highest energy orbital of the base will react with the lowest energy orbital of the acid

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26
Q

What does a + charge represent on a nitrogen?

A

Loss of lone pair

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27
Q

What does a + charge on a carbon represent?

A

Loss of a bond (2 electrons)

28
Q

When an alkene reacts with HBr which carbon does the H attach to?

A

The carbon that is connected to the most hydrogens, this is because the other carbocation becomes the carbocation and this is more stable when there are more alkyl groups attached to it as alkyl groups are electron donating which reduces the positive charge of the carbocation

29
Q

When an alkene reacts with HBr how is the reaction started?

A

Energy is required to start the reaction, the activation energy of the reaction is slightly higher than the energy of the carbocation intermediate. The less energy the carbocation has the more stable it is and the less energy required to start the reaction. The overall reaction is exothermic as the overall energy of the system decreases.

30
Q

Describe how an NO2 group is attached to a benzene ring by electrophilic substitution

A

One of the double bonds on the benzene attacks the positive charge on the N, this leaves NO2 and an H atom attached to the same carbon and leaves a carbocation (the adjacent carbon), a base is then needed to react with the hydrogen. The base attacks the hydrogen and the electron flow is moved from the bond between the hydrogen and carbon to the bond between the two carbons which forms a double bond again. This means that NO2 is now attached and a compound of the hydrogen and base is formed

31
Q

What is an SN2 mechanism?

A

A reaction mechanism where there are two molecules in the RDS, the rate equation will have the concentrations of two molecules in it

32
Q

How does the SN2 mechanism work?

A
  • A nucleophile attacks the electrophile and pushes out the leaving group
  • The nucleophile attacks from behind the C-X bond, this inverts the molecule
  • SN2 reactions occur in one step, there is a point in the reaction where the molecule is in a transition state which is where the nucleophile is attached but the leaving group is also still attached, this is drawn by showing the nucleophile and leaving group attached by dotted lines
33
Q

What is an SN1 mechanism?

A
  • A reaction mechanism where only one molecule is involved in the rate determining step
  • The nucleophile is not involved in the RDS
34
Q

How does the SN1 mechanism work?

A
  • The nucleophile attacks the C-X bond in the second step of the reaction which is why it doesn’t appear in RDS
  • The nucleophile can attack the molecule from either side of the C-X bond as there is an empty p orbital
  • If it attacks from behind the C-X bond then the product is inverted, if it attacks from in front then the molecule is not inverted
35
Q

Why is a racemic mixture formed when an SN1 mechanism occurs?

A

Depending on which side the nucleophile attacks the empty p orbital from, a different enantiomer is formed. As the nucleophile is just as likely to attack from either side, a racemic mixture is formed as an equal amount of each enantiomer is formed

36
Q

What is the standard rate equation for an SN1 equation?

A

Rate = k [R3C-X]

37
Q

What is the standard rate equation for an SN2 equation?

A

Rate = k [R3C-X] [Nu-]

38
Q

Why does an SN1 mechanism occur?

A
  • Nucleophile may not be reactive enough to react with Cδ+

- C-X may be a very weak bond and break easily

39
Q

What happens to the activation energy of an SN1 reaction as the amount of alkyl groups attached to the carbocation increases?

A

The activation energy decreases as the carbocation intermediate is lower energy. The activation energy is always slightly higher than the energy of the intermediate hence the activation energy decreases.

40
Q

Can bromobenzene undergo an SN1 or SN2 mechanism?

A
  • It can’t undergo an SN2 mechanism as the π-system is too electron rich so the carbon in the ring can’t be attacked
  • It also can’t undergo SN1 as the C-Br bond can’t be broken as the carbocation that would be produced is very unstable. This is because the C-Br bond was an sp2 bond and therefore the positive charge is also in a sp2 orbital. This charge is very localised and the carbocation is too unstable
41
Q

As a carbon cation becomes more stable, what happens to the speed of an SN1 reaction?

A

It increases as less energy is required to reach the intermediate

42
Q

What happens to the speed of SN2 reactions as the Cδ+ becomes less crowded?

A

Reaction becomes faster as Cδ+ becomes less crowded as the nucleophile has better access to the carbon sterically

43
Q

How do you predict whether an SN1 or SN2 mechanism will take place?

A

If the carbocation is stable, eg. has +M effect or is tertiary then SN1 will take place, if not SN2 will

44
Q

What is the order of priority for leaving groups?

A

I- > H2O > Br- > Cl- > F- > OH-

45
Q

Give examples of polar protic solvents

A

H2O, CH3OH, CH3COOH

46
Q

Give an example of polar aprotic solvents

A

(CH3)2S=O, CH3CN

47
Q

Give an example of non-polar aprotic solvents

A

Et2O and Hexane

48
Q

What does increasing the strength of a nucleophile or increasing the concentration of a nucleophile do to an SN1 and SN2 reaction?

A
  • It doesn’t do anything to an SN1 reaction as the nucleophile isn’t part of the RDS, it increases the rate of an SN2 reaction
  • However if two nucleophiles of different strength are competing in the same SN1 reaction then the stronger nucleophile will form the major product and the weaker one will form the minor product
49
Q

Why are polar solvents required for SN1 and SN2 reactions?

A

To dissolve the ionic reactants, also in SN1 reactions polar solvents stabilise the carbocation

50
Q

What does increasing the polarity of the solvent do to the rate of an SN2 reaction when using a negatively charged nucleophile?

A

Increasing the polarity slightly decreases the rate of reaction of an SN2 mechanism as the polar solvent solvates the nucleophile better than it solvates the large transition state. The more polar the solvent the more solvated the nucleophile and therefore the slower the SN2 reaction.

51
Q

What does increasing the polarity of the solvent do to the rate of SN2 reaction when using an uncharged nucleophile?

A

It increases the rate of SN2 reaction as it solvates the transition state better than the nucleophile, this means that as you increase the polarity, the transition state becomes more stable

52
Q

Why are aprotic solvents favoured for SN2 reactions?

A

As aprotic solvents can’t solvate negatively charged nucleophiles by forming hydrogen bonds with them, this means that the reactivity of the nucleophile isn’t reduced by the aprotic solvent and the nucleophile is free to react with the haloalkane

53
Q

What happens to the rate of reaction as you increase the polarity of the solvent in an SN1 reaction

A

Increasing the polarity of the solvent results in a significant increase the rate of reaction of an SN1 reaction as the polar solvent solvates the carbocation which makes it more stable and therefore as polarity increases the stability of carbocation increases and rate of reaction also increases

54
Q

How does the C-X bond break in an SN1 reaction?

A

If the bond isn’t extremely weak then the bond will need energy from solvation

55
Q

Why is a protic solvent favoured for SN1 reactions?

A

The protic solvent stabilises the halide ion that is formed from the heterolytic cleavage of the C-X bond

56
Q

What happens to the rate of reaction when you change from a polar protic to an polar aprotic solvent in an SN1 reaction?

A
  • The rate of reaction is decreased as the polar protic solvents solvates both the carbocation and the halide ion whereas the polar aprotic only solvates the carbocation
  • Although the polar protic solvent solvates the nucleophile and makes it less reactive this doesn’t affect the rate of reaction as the Nucleophile isn’t involved in the RDS
57
Q

When a secondary carbocation is formed by the breaking of the C-X bond and the other carbon has 3 methyl groups attached, what may happen to make the carbocation more stable?

A

One methyl group may move to the other carbon, this means that the carbon that has lost the methyl group is now the carbocation and it is tertiary because it has 2 methyl groups attached and is connected to another carbon

58
Q

What happens to the inductive effect when there is a multiple carbon chain attached to an electronegative element?

A

The carbons further back in the cahin donate their electron density towards the electronegative atom, the carbon at the front of the chain will be δ+ and the carbon behind will be δδ+ and so on

59
Q

What is a better nucleophile out of iodine and chlorine?

A

Iodine as it is less electronegative meaning it is more willing to give away its negative charge, it is also more polarisable meaning it makes stronger bonds

60
Q

Why is iodine the best leaving group out of all the halogens?

A

As it is the largest atom meaning the charge density is decreased and it is the most stable when it accepts electrons to form an ion

61
Q

Are amines better nucleophiles than ammonia?

A

Yes, due to the -I effect that the R groups have, the amine is a better nucleophile as it has a greater negative charge than ammonia. However if the R groups are too large then the amine may be too large to be a better nucleophile than ammonia

62
Q

Which is the most acidic out of OH, NH and NH2

A

OH as it best stabilises the negative charge that you get when you lose the hydrogen. This is because it is the most electronegative so the O is more stable with a negative charge

63
Q

How does resonance effect nucleophiles?

A

If a nucleophile is experiencing a -M effect then the reactivity of the nucleophile is decreased as electron density is pulled away

64
Q

The carbonyl with which substituent attached out of these is the most reactive as an electrophile: Cl, H, CH3, OR, NR2

A
  • Cl is the most reactive as it has a -I effect and withdraws electrons from the carbon meaning the δ+ on the carbon is increased
  • H is next reactive as it has no effect on the δ+
  • CH3 is the next reactive as it has a +I effect meaning it donates electrons to the carbon meaning δ+ is reduced
  • OR is next reactive as it donates electrons to the carbon as it has a +M effect. The +M effect is more significant than +I meaning that the δ+ charge is weaker with OR than CH3
  • NR2 is the least reactive as it has a stronger +M effect than OR as N is less electronegative than O meaning it donates electrons more willingly so the δ+ is reduced the most
65
Q

Which carbon will H- attack on CH3COCH2COOCH3?

A

It will attack the first carbon as it only has a +I effect rather than a +M effect from the OCH3. This means that the first carbon is more nucleophilic and therefore more susceptible to attack from H-

Year 1 Chem (7 decks)

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