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GAMSAT March 2016 > Org 6 - Alcohols > Flashcards

Org 6 - Alcohols Flashcards

1
Q

What is an alcohol ?

A

Any organic compound in which a hydroxyl group (OH) is bound to a carbon atom of an Alkyl or substituted alkyl group.

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2
Q

What is the general formula of an alcohol ?

A

R-OH

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3
Q

Explain how alcohols are classified ?

A
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4
Q

How are the carbons in an alcohol numbered ?

A

The alcohols are always numbered to give the carbon with the hydroxy (OH) group the lowest number

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5
Q

What is the prefix for a 5 carbon chain ?

A

Pent

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6
Q

What is the prefix for a 6 carbon chain ?

A

Hex

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7
Q

What is the prefix for a 3 carbon chain ?

A

Prop

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8
Q

When oxygen is bonded R-OH, how many lone E- pairs does it have ?

A

2 lone pairs

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9
Q

Explai hydrogen bonding in alcohols ?

A

The partially positive hydrogen in one molecule is attracted to the partially negative oxygen in another molecule.

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10
Q

Explain why methanol has a lower boiling point than water ?

A

2 partially positive hydrogens in each H20 are available to hydrogen bond, but only 1 partially positive hydrogen in an alcohol (due to R groups)m which means that the hydrogen bonding is easier to break.

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11
Q

Explain the boiling point and solubility trends of alcohols ?

A
  • Higher boiling points and greater solubility tha comparable alkanes, alkenes, aldehydes, ketones and alkyl halides
  • This is due to greater polarity and hydrogen bonding
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12
Q

Explain the pH trend of alcohols ?

A
  • Decreases with increasing number of attached carbons
  • Primary > Secondary > tertiary
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13
Q

What is the name of an alcohols conjugate base ?

A

An alkoxide

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14
Q

Are alcohols basic or acidic ?

A

They are weak acids

(weaker than water)

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15
Q

What does miscible mean ?

Give an example

A

Soluble in water in any proportion

e.g. Methanol is miscible in water, butanol is slightly soluble but not miscible

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16
Q

Why do alcohols become less soluble as the length of the Carbon chain (R Group) increases ?

A

The R group is non-polar, thus inhibiting the molecules ability to hydrogen bond.

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17
Q

Describe the acidity and basicity of alcohols

A

Alcohols can dissociate into a proton and its conjugate alkoxide.

As weak acids, alcohols act as proton donors:

ROH + H2O → RO - + H3O+

As weak bases, alcohols act as proton acceptors:

ROH + HX → ROH2+ + X-

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18
Q

Describe the effect of substituents on alcohol acidity

A

The more easily the alkoxide ion is accessible to H2O, the easier it is stabilised through solution, therefore the more its formation is favoured leading to greater acidity.

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19
Q

Describe the influence of inducting effects on alcohol acidity ?

A
  • E- withdrawing groups stabilise an alkoxide ion by spreading out the charge, therefore making the alcohol more acidic.
  • E- donating groups destabilise the an alkoxide anion, making the alcohol less acidic.
20
Q

Descibe the difference in boiling point between ethane(g) and ethanol(l) ?

A
  • Ethane has a low boiling point as only very weak London (VDW) forces are holding the molecule together.
  • Ethanol has a higher boiling point due to hydrogen bonding formation
21
Q

Describe an alcohols reaction with a base ?

A
  • Alcohols are only weak acids, therefore they do not react with weak bases
  • Alcohols react with strong bases such as NaH or Na or K metals
22
Q

Explain the 3 ways alcohols can be synthesised ?

A
  1. Hydration of Alkenes
  2. Reduction of Carbonyl compounds
  3. Addition reactions with Grignard reagents
23
Q

What Carbonyl compounds can be reduced to give alcohols ?

A
  • Aldehydes
  • Ketones
  • Carboxylic acids
  • Esters
24
Q

What does LiAlH4 reduce aldehydes and ketones to ?

A

Aldehydes ⇒ 1º Alcohols

Ketones ⇒ 2º Alcohols

Esters ⇒ 3º Alcohols

25
Q

Name 5 important reactions of Alcohols ?

A
  1. Dehydration
  2. Oxidation-reduction
  3. Substitution
  4. Elimination
  5. Conversion to Alkyl Halides
26
Q

What do dehydration reactions of alcohols produce ?

A

Dehydration = loss of water, therefore alkenes are produced

27
Q

What does ‘R’ represent in organic chemistry ?

A

Denote attached hydrogen or hydrocarbon side chains of any length

28
Q

Describe Oxidation

A

The increasing of oxygen or decreasing of hydrogen

OIL

Oxidation Is Loss

29
Q

Describe reduction

A

The decreasing of oxygen or increasing of hydrogen

RIG

Reduction Is Gain

30
Q

Under mild and abrasive conditions, what are primary alcohols oxidised to ?

A

Mild ⇒ Aldehyde

Abrasive ⇒ Carboxylic Acid

31
Q

What are secondary alcohols oxidised to form ?

A

Ketones

32
Q

Explain oxidation of tertiary alcohols

A

Tertiary alcohols are very difficult to oxidise, they are unaffected by acidic conditions.

33
Q

What is meant by the term substitution reaction ?

A

One atom or group is replaced by another.

E.g. In alcohols, the OH group can be substituted by a halide (Usually Cl or Br)

34
Q

Describe the term ‘Sn1 Reaction’

A
  • 1st order, or macromolecular (nucleophilic substitution)
  • The transition state involves a carbocation, the formation of which is the rate determining step.
35
Q

What Alcohol substitutions usually proceed by Sn1 ?

A

Reactions involving Benzyl groups, alkyl groups, tertiary and secondary alcohols.

36
Q

Name 3 important features of an Sn1 reaction ?

A
  1. The reaction is 1st order (rate depends on concentration of 1 compound)
  2. There is racemization of configuration when a chiral molecule is involved
  3. A stable carbonium ion should be formed
37
Q

What is an Sn2 reaction ?

A

2nd order or bimolecular nucleophilic substitution

38
Q

Name 3 important points regarding Sn2 reactions ?

A
  • The reaction rate is second order overall (rate depends on concentration of 2 compounds)
  • The nucelophile adds to the alkyl group at the opposite side to the ligand
  • Large or bulky groups near or at the site may hinder or retard a reaction (Steric hindrance)
39
Q

Explain steric hindrance

A
  • Large or bulky groups near or at the reacting sites hinder or retard the rate of Sn2 reactions
40
Q

What reactions involving alcohols proceed via the Sn2 mechanism ?

A

Substitution reactions for Methanol and other primary alcohols

41
Q

Explain good leaving groups in organic chemistry ?

A

Good leaving groups have strong conjugate acids

E.g H2O because H3O+ is a strong acid.

42
Q

What is an elimination reaction ?

A

When an atom or group of atoms is removed (eliminated) from adjacent carbons leaving a multiple bond.

43
Q

Describe E1 reactions ?

A
  • The rate depends on the concentration of one compound
  • Often occurs as minor products alongside Sn2 reactions
44
Q

What would happen if you double the concentration of both reactants in an Sn2 reaction ?

A

In a second order reaction, the rate is proportional to the concentration of both reactants, therefore if both the concentrations were doubled, the rate would increase four-fold.

45
Q
A

GAMSAT March 2016 (26 decks)

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