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Organic Chemistry Year 12 > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

what is functional group of alcohols

A

-OH (hydroxyl)
- is responsible for physical and chemical properties

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2
Q

what is difference between displayed, structural, shortened structural and molecular formula of alcohols

A
  • DISPLACED= show ALL bonds, including the O-H BOND!!
  • STRUCTURAL= show detail of how atoms bonded, e.g. CH3CH2CH2OH
  • SHORTENED STRUCTURAL= shows the OH group at end, e.g. C3H7OH
  • MOLECULAR= just shows amount of each atom present, e.g. C3H8O
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3
Q

what is the general formula of alcohols

A

CnH2n+1OH

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4
Q

how do you name alcohols based on the IUPAC names

A

1) count longest carbon chain to decide prefix
2) count the number of OH groups to determine suffix (-ol, -diol, -triol, -tetraol), remembering to not shorted alkane name if suffix doesn’t start with a vowel, e.g. 2-methylbutane-2,3-biol
3) number the chains with OH group, which take priority over methyl group number
4) name and number alkyl groups, remembering that they go in alphabetical order

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5
Q

how do you classify alcohols

A
  • based off the number of carbon and hydrogen atoms attached to the carbon with -OH
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6
Q

what are the 3 classes of alcohols

A

1) primary- has 1 carbon atom attached and 2 hydrogens - ALWAYS ethanol, and METHANOL, which is exception, as has 0 C’s and 3 H’s, but still classed
2) secondary- has 2 alkyl groups attached, and 1 H
3) tertiary- has 3 alkyl groups attached, and 0 H’s

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7
Q

what are the properties when comparing alcohols with their corresponding alkanes (same number of C atoms)

A
  • less volatile
  • higher melting points
  • greater solubility in water
  • differences become less as length of the carbon chain increases
  • ALL DUE TO THE O-H BOND
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8
Q

explain what is responsible for the properties of alcohols

A
  • have polar O-H bond, as O is more electronegative than H, so are polar molecules
  • have weak LDF, BUT also have stronger hydrogen bonding between the O-Hs
  • whereas alkanes have no polar bonds, as C and H have similar electronegativities, so non-polar molecules, with only weak LDF
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9
Q

why are alcohols less volatile than alkanes

A

volatile = ability to change from liquid to gas, so have HIGH boiling point
- to go from liquid to gas, the stronger hydrogen bonds need to be broken
- so more energy required than LDF in alkanes

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10
Q

explain the solubility of alcohols

A
  • can form hydrogen bonds with water molecules
  • between polar O-H bond and water

-BUT, as hydrocarbon chain increases, the influences of the -OH bond decreases, so solubility decreases

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11
Q

explain the viscosity of alcohols

A
  • as you increase the number of OH groups in alcohol
  • the more hydrogen bonding
  • so stronger attraction
  • and more viscous
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12
Q

explain the combustion of alcohols

A
  • burn in plentiful supply of oxygen to form CO2 and H2O
  • if incomplete, CO and C will be formed too
  • exothermic, as releases a lot of energy in form of heat
  • as the number of C atoms in the chain increases, so does the heat released per mole
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13
Q

how are alcohols formed

A
  • reaction of alkene and steam
  • needs high temperature, pressure, and presence of concentrated H3PO4 catalyst
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14
Q

what is an alternate way to form alcohols

A
  • via formation of sugars from plant carbohydrates
  • e.g. C6H12O6 ===> 2C2H5OH + 2CO2
  • needs to be room temp, anaerobic and enzyme catalyst
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15
Q

what are the 3 reactions of alcohols

A
  • oxidation
  • dehydration
  • substitution
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16
Q

which alcohols can be oxidised

A

primary and secondary, by an oxidising agent

17
Q

what is the oxidising mixture you put on the arrows

A
  • potassium dichromate (VI) - K2Cr2O7
  • acidified with dilute sulfuric acid - H2SO4
18
Q

what is the colour change for a successful oxidation of alcohols

A

colour change of orange to green

  • due to going from dichromate ions (Cr2O7 2-) to chromium ions (Cr3+)
19
Q

how can primary alcohols initially be oxidised

A
  • heated gently and distilled to form aldehyde
    -distillation prevents further reactions with oxidising agent, which would cause carboxylic acid to form
  • primary alcohol + [O] ===> aldehyde + H2O
20
Q

how can primary alcohols be further oxidised

A
  • if heated strongly unser reflux, with an excess of K2Cr2O7, a carboxylic acid is formed
  • under reflux so that any aldehyde initially formed undergoes oxidation into CA too
  • with excess of K2Cr2O7 to ensure all of alcohol has been oxidised

primary alcohol/aldehyde + [O] ===> carboxylic acid + H2O

21
Q

how would I alter experiments of oxidation of primary alcohols depending on the product i wanted

A
  • if aldehyde wanted, gently heat and distil
  • if carboxylic acid wanted, heat strongly under reflux
22
Q

how can secondary alcohols be oxidised

A
  • heated under reflux to form ketone
  • does not undergo further oxidation to form anything else like aldehydes
  • under reflux to ensure the reaction is complete

secondary alcohol + [O] ===> ketone + H2O

23
Q

what oxidation to tertiary alcohols go through

A
  • none, so the acidified dichromate (VI) remains orange in presence
24
Q

how do alcohols go through dehydration

A
  • an elimination reaction where water molecule is removed (OH and H next to it)
  • produces an alkene
  • ONLY possible if there is H atom on the carbon adjacent to the carbon with the OH group attached
  • heated strongly under reflux (170 degrees celsius)
  • presence of an acid catalyst: H3PO4 or H2SO4
25
Q

explain the multiple products formed from the dehydration of butan-2-ol

A
  • but-1-ene
  • trans-but-2-ene
  • cis-but-2-ene
26
Q

form the substitution reaction of alcohols

A
  • react with hydrogen halides (e.g. bromide and chloride)
  • forms haloalkanes
  • heated under reflux, with dilute H2SO4 and SODIUM HALIDE
  • halide used determines the hydrogen halide reacted with (formed in situ, in place of) , determining product
27
Q

explain the 2 reactions of substitution of alcohols, imagine using sodium bromide

A

NaBr(s) + H2SO4(aq) ===> NAHSO4(aq) + HBr(aq)

alcohol + HBr ===> haloalkane + H2O

28
Q

what is the overall reaction for substitution of alcohols

A

alcohol + NaBr + H2SO4 ===> haloalkane + NaHSO4 + H20

  • hydrogen bromide produced disappears
29
Q

equation for percentage yield

A

actual yield / theoretical yield x100

  • all qualities must be IN MOLES
30
Q

what is the limiting reagent

A

the reactant that is not in excess and will get used up completely first and stop the reaction

  • USE THIS TO CALCULATE MOLES OF PRODUCT PRODUCED
31
Q

what is atom economy

A

measure of how well the atoms have been utilised

RFM of desired product / sum of RFMs of all products x100

  • to lower, have more useful products, or lower the RFMs of waste products by using different reaction

Organic Chemistry Year 12 (6 decks)

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