9 Alcohols Flashcards
What is the functional group of aliphatic alcohols?
a hydroxyl group (-OH) bonded to an sp3-hybridized carbon
What are ‘-enol’ compounds?
compounds with the hydroxyl group attached to an unsaturated (sp2) C=C carbon atom
Draw out two examples of aliphatic alcohols.
see document
Draw out an enol and a phenol.
see document
What are alcohols classified according to?
the environment of the OH group
What does the chemical behaviour (e.g. oxidation and reaction mechanisms) of an alcohol depend on?
on the structural type of alcohol
For alcohols 1-3 state:
a) the name of the alcohol
b) the classification of the alcohol
a)
1 - 1-butanol
2 - 2-butanol
3 - 2-methyl-propan-2-ol
b)
1 - primary alcohol
2 - secondary alcohol
3 - tertiary alcohol
State the process of IUPAC naming alcohols.
select the longest chain of carbon atoms containing the -OH group
remove the ‘-e’ and add ‘-ol’ after the basic name
number the chain starting from the end nearer to the -OH group
the number is placed after the ‘-an’ and before the ‘-ol’ (e.g. butan-2-ol)
as in alkanes, prefix with alkyl substituents
side-chain positions are based on the number allocated to the -OH group
State the process common naming of alcohols.
name the alkyl group bonded to oxygen followed by the word alcohol
For alcohols 1-6 state:
a) the IUPAC name
b) the common name (i.e. ‘-yl alcohol’ and then primary = iso, secondary = sec and tertiary = tert)
a) IUPAC names: 1 - propan-1-ol/ 1-propanol 2 - propan-2-ol/ 2-propanol 3 - butan-1-ol/ n-propanol 4 - butan-1-ol/ sec-butanol 5 - 2-methyl-propan-1-ol 6 - 2-methyl-propan-2-ol/ tert-butanol
b) common names: 1 - propyl alcohol 2 - isopropyl alcohol 3 - butyl alcohol 4 - sec-butyl alcohol 5 - iso-butyl alcohol 6 - tert-butyl alcohol
How are compounds containing more than one -OH groups named?
named as diols, triols, etc…
For compounds 1-3 (on document) with multiple -OH groups state:
a) the IUPAC name
b) the common name
a) 1 - ethane-1,2-diol/1,2-ethanediol 2 - propane-1,2-diol/1,2-propanediol 3 - 1,2,3-propanetriol/propane-1,2,3-triol b) 1 - ethylene glycol 2 - propylene glycol 3 - glycerol/glycerine
What type of compounds are alcohols?
polar compounds
What type of boiling points do alcohols have and why?
much higher than comparable hydrocarbons and ethers
due to hydrogen bonding
Draw out a diagram showing hydrogen bonding between 4 methanol molecules including lone pairs.
see document
Draw out the bonding between a model methanol molecule including the lone pairs.
see document
How soluble are (small) alcohols and why?
lower (smaller) alcohols (and ethers) are water-soluble
due to hydrogen bonding with water
What does hydrogen bonding mean for the use of alcohols in terms of other organic molecules?
good solvents for a wide range of organic molecules
What do the boiling points of alcohols increase with?
increase with the number of carbon atoms/lenghth of carbon chain
What are the 3 properties of the ‘electron-rich’ and ‘nucleophilic’ oxygen atom in alcohols?
- lone-pair donors (Lewis bases)
- proton acceptors (Bronstead-Lowry bases)
- nucleophilic (lone pair attacks electron-deficient centres)
(see document for this)
What can most alcohols not classed as but are able to act as?
most alcohols are not weak acids
but H⁺ can be removed by a strong base or reaction with a strong metal
What property do the electron-deficient C and H atoms in alcohols have?
they are attacked by electrophiles
State how alcohols are synthesised by ‘hydration’ by ‘Markovnikov addition’ of alkenes, including:
a) reagents
b) conditions
(Hint: Markovnikov = major product)
a) H₂O and conc. H₂SO₄ (or another acid catalyst)
b) heat
State how alcohols are chemically synthesised by ‘hydration’ by ‘Anti-Markovnikov’ addition of alkenes, including:
a) reagents
(Hint: anti-Markovnikov = minor product)
a) step 1: BH₃
step 2: + H₂O₂
Give an example of a ‘Markovnikov addition’ reaction of prop-1-ene (draw out the molecules too).
(see document)
Give an example of a ‘anti-Markovnikov addition’ reaction of prop-1-ene (draw out the molecules too).
(see document)
Give an example of a ‘hydration’ reaction in the citric acid cycle (draw out the molecules too) and name the enzyme involved.
The step in beta-oxidation of fatty acids in mitochondria or peroxisome
RCH₂CH(OH)CH₂COSCoA + H₂O → RCH₂CH=CHCOSCoA
(Enzyme: enoyl-CoA Hydratase)
R = CH₃, CH₃CH₂… etc…
(see document for drawings)
State how alcohols are chemically synthesised by ‘substitution of alkyl halides’ including:
a) reagents
b) conditions
c) the general reaction equation
a) NaOH, H₂O
b) heat
c) R-X + NaOH → R-OH + NaX
What do all organometallic reagents have?
a nucleophilic carbon
What is a ‘Grignard reagent?’ (Hint: Grind = being mixed, X = Cl, Br, etc…)
R⁺-MgX (where X = Br, Cl (halide))
What is ‘Organolithium?’ (Hint: R = by itself/organic/all natural)
R⁺-Li (lithium alkyl)
State how alcohols are chemically synthesised using carbonyls by ‘addition of organometallic to aldehydes/ketones’ in 2 steps including:
the full reaction equation
a) reagents
b) conditions
R-C=O-R₂ + R₃-MgX → R(-R₂ )-C-R₃(-O-MgX) → R-R₂ -C-R₃(-OH)
(see document for symbol equation)
step 1:
a) R₃-MgX
b) N/A
step 2:
a) N/A
b) H⁺/H₂O
State how alcohols are chemically synthesised using carbonyls by ‘reduction of an aldehyde/ketone’ including:
the full reaction equation and:
a) reagents
(Hint: for 1 O atom 1 metal in the reducing agent)
R-C=O-R₂ → R-C(-OH)-R₂
a) NaBH₄
State how alcohols are chemically synthesised using carbonyls by ‘reduction of a carboxylic acid/ester’ including:
a) reagents
b) the second less significant product also made
(Hint: for 2 O atoms 2 metals in the reducing agent)
R-C=OO-R₂ → R-C(-OH) + HO-R₂
a) LiAlH₄
c) R₂-OH (alcohol)
Give an example of a biological ‘reduction of carbonyl’ reaction in the citric acid cycle (draw out the molecules too) and name the enzyme involved.
Dihydroxyacetone → (S)-glycerol phosphate
enzyme = NAD(P)H
(see document for diagram)
What are ‘mono-oxygenase’ enzymes?
enzymes that incorporate one hydroxyl group into substrates in many metabolic pathways
Give an example where ‘mono-oxygenases’ are used in biosynthesis.
consists of 2 steps
enzyme for step 1 = CYP450
end-product = cortisol (enzyme)
(see document for structures)
Using an example, explain how ‘drug metabolism’ is used in biosynthesis.
tamoxifen → more active metabolite
(CYP3A4, 2C9, 2D6)
(see document for structures)
For each of the following compounds a-c (see document) draw the product if it reacts with:
a) + aq. H₂SO₄
b) + NaBH₄
c) + LiAlH₄
a) pentan-2-ol
b) N/A (no reaction as NaBH₄ is not strong enough to reduce an ester)
c) pentan-1,5-diol
For the 3 ways that alcohols chemically react to produce alkyl halides, write out the full general reaction equations:
(Hint: RX usually made + HX too sometimes)
a) reaction with thionyl chloride
b) reaction with HX (acids)
c) reaction with phosphorus halides
a) ROH + S=OCl₂ → RCl + SO₂ + HCl
b) ROH + HX → RX + H₂O
c) ROH + PX5 → RX + POX₃ + HX
3ROH + PX₃ → 3RX + H₃PO₃
State the reagents for the two substeps of the reaction between alcohols and phosphorus halides.
step 1: S=OCl₂
step 2: Sn2
Draw out the mechanism for the general reaction between an alcohol and a phosphorus halide.
(include alkyl groups as R and curly arrows to represent the movement of electrons)
(see document for this)
State how alkenes can be chemically synthesised using dehydration including:
a) reagents
b) conditions
a) H₂SO₄
b) 180°C (heat)
(see document for the diagram of ethene production)
State a biological example of 2-step alkene synthesis using dehydration, including:
a) the final product
b) enzymes
a) prephenate → 4-hydroxyphenylpyruvate → tyrosine (product)
b) dehydroquinate dehydratase
What is another name for reacting alcohols with carboxylic acids?
esterification
State the general reaction for chemical synthesis of an ester.
R-OH + R-C=O(OH) ⇌ R-C=OOR + H₂O
Give an example of biological esterification involving acetyltransferases/esterases.
glycerol-3-phosphate → 1-acylglycerol-3-phosphate
(acetyltranferase)
(RC=O(SCoA))
What type of reaction is ‘ether synthesis?’
substitution
State how an ether can be chemically synthesised from alcohol in 2 steps using ‘William ether synthesis.’
a) reagent of the 2nd step
R-OH + Na → RO-Na⁺ → R-O-R’ + NaX
alcohol ether
a) R’X
What is ‘methylation’ and what can SAM (S-Adenosyl methionine) do?
Adding a CH3 group to a molecule
It is not just a reaction of alcohols SAM can methylate C, N, S
Give an example of a biological ether production by methylation with SAM. Include:
a) reagents
b) the enzyme
see document for this
a) S-adenosyl methionine
b) methyl transferase
How can primary alcohols (i.e. RCH₂OH) be oxidised?
→ aldehyde → carboxylic acid
→ RCHO → RCOOH
Give an example of biological oxidation of a primary alcohol. State the reagents for each step and draw out the structures.
ethanol → acetaldehyde → acetic acid
reagent: Na₂Cr₂O7
(see document for this)
How can secondary alcohols (i.e. RCH₂OH) be oxidised?
secondary alcohol → ketone
Give an example of biological oxidation of a secondary alcohol. State the reagents for each step and draw out the structures.
isopropanol → acetone
reagent: Na₂Cr₂O7/H⁺
(see document for this)
How can tertiary alcohols be oxidised?
they cannot be oxidised
Why can tertiary alcohols not be oxidised?
for oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms
possible in primary and secondary alcohols, but not in tertiary ones
For each of the alcohols (on the document) a-c state name and draw out the product.
a) Acetaldehyde
b) Acetone
c) No product
Write out the balanced equation for the partial oxidation of ethanol using [O] to represent the oxidising agent.
CH₃CH₂OH + [O] → CH₃CHO + H₂O
ethanol ethanal
Which conditions are required in the lab for primary oxidation of alcohols?
essential to distill off the aldehyde before it gets oxidised to the acid
Write out the balanced equation for the oxidation of ethanal using [O] to represent the oxidising agent.
CH₃CHO + 2[O] → CH₃COOH + H₂O
ethanal ethanoic acid
State the practical details to oxidide an alcohol to an aldehyde (and draw the apparatus involved).
the alcohol is dripped into a warm solution of acidified K₂Cr₂O7
aldehydes have low boiling points - no hydrogen bonding - they distill off immediately
if
What would happen if a primary alcohol wasn’t distilled off as soon as it is oxidised to an aldehyde?
it would be oxidised to the equivalent carboxylic acid
State the practical details to oxidise an alcohol into a carboxylic acid (and draw the apparatus involved).
So, to oxidise an alcohol straight to the acid, reflux the mixture
What colour do dichromate ions change to during the oxidation of primary alcohols?
from orange to green
For each of the following compounds state the intermolecular bonding to justify the boiling points:
a) ethanol, C₂H5OH, 78°C
b) ethanal, CH₃CHO, 23°C
c) ethanoic acid, CH₃COOH, 118°C
a) hydrogen bonding
b) dipole-dipole bonding
c) hydrogen-bonding
Give using the example of ethanol the reaction equation for biological oxidation stating (and drawing) the cofactors involved.
NAD⁺ NAD⁺
ethanol ⇌ acetaldehyde ⇌ acetic acid
NADH NADH
Zn2+
(see document for strcutures of compunds and of NAD/NAD⁺)
Draw out the 3 pathways for the biological exmaples of oxidation of alcohols (ethanol, methanol and ethylene glycol).
(Hint: first 2 = can-openers)
see document for this
State the hybridisation of oxygen atoms within an alcohol and use it to explain its domain geometry.
Two sp3 hybrid orbitals form sigma bonds to carbon and hydrogen
The remaining two sp3 hybrid orbitals each contain an unshared pair of electrons
Domain geometry about the hydroxyl oxygen atom approximately 109° - repulsion of lone pairs vs size of sidechains
(see document for diagram of this answer)
