Year 1: Foundation chem WREN

What are alcohols?

What are alcohols?

Compounds with one or more -OH group attached to a hydrocarbon group

Explain the role of hydrogen bonding in alcohols

• Strong dipole-dipole interactions

• Between the highly polarised O-H bond + lone pairs of electrons on oxygen

State the 3 physical properties on the effect of hydrogen bonds

• Difference in boiling points

• Solubility of ethanol in water

• Broadening of OH peaks in infrared spectra

Explain the difference in boiling points of alcohols

• Caused by the presence or absence of hydrogen bonding

• Eg- ethanol and dimethyl ether are isomers with the same RMM but ethanol had hydrogen bonding thus a higher boiling point

Explain the physical property of the solubility of ethanol in water

• Ethanol has an infinite solubility in water

• In other alcohols, solubility DECREASES as the R group becomes LARGER

State the 5 methods used to synthesise alcohols

• Substitution of haloalkanes

• Via Grignard reagents

• Reduction of carbonyl compounds

• Hydration of alkenes

• Fermentation

Outline and state the mechanism used for the substitution of haloalkanes

DRAW THE MECHANISM

• primary haloalkanes

• Warm,aqueous NaOH

Draw how gringnard reagents are used to prepare alcohols

• Grignard reagent is formed with a Mg metal

• The Grignard reagent forms a tertiary alcohol

• Nucleophilic addition of GR to the carbonyl group

What does a Grignard reagent and methanal lead to?

DRAW THE MECHANISM

• 1 alcohol

What does a gringard reagent and a ketone lead to?

• Tertiary alcohol

During the reduction of carbonyl compounds what can they lead to?

• Aldehydes and ketones may be reduced to give 1 and 2 alcohols

What are the 2 ways in which carbonyl groups are reduced?

• Catalytic hydrogenation (H2/Ni/pressure)

• Hybride reducing agents

What is the most favourable hybride reducing agent used and why?

• NaBH4

• Less reactive and can be used safely in water

Draw the mechanism for how NaBH4 reduces a carbonyl compound

Draw and state mechanism for how 2-methylpropene forms an alcohol

State the reagent

• H2SO4

• Electrophilic addition

What is the markinov addition?

• The H is added to the carbon atom which has the greater number of H atoms already

What is an anti-markovnikov product?

• H atom is added to the carbon atom which has the lowest number of H atoms already

Explain how fermentation produces alcohols

• Fermentation of sugars gives an aqueous solution of ethanol

• Enzyme used is yeast and is inactivated

• They catalyse the conversion of sugars into alcohol and carbon dioxide

State what an Sn1 mechanism is and give an example

• Weak nucleophiles

• Form a carbocation intermediate

• The solvent replaces the leaving group

State what the Sn2 mechanism is and draw the mechanism

• Strong nucleophiles

• Bimolecular nucleophilic substitution where 2 molecules are reacting at the same time

• No carbocation intermediate

• Nucleophile directly replaces the leaving group

State what the E1 mechanism is and draw the mechanism

• Elimination reaction

• Uses heat to favour elimination rather than nucleophilic substitution

• Has a carbocation intermediate

• Double bond forms between A+B carbons

State what the E2 mechanism is and draw the mechanism

• Bimolecular elimination

• Uses heat to favour an elimination reaction rather than nucleophilic substitution

• No carbocation intermediate

• Double bond forms between a and b carbons

Previously, we discussed that the secondary alcohol shown below can be synthesised by reacting 2-phenylethanal (C₆H₅CH₂CHO) with methyl magnesium bromide (CH₃MgBr), followed by treatment with aqueous acid.

 

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       If the same 2^o alcohol is heated with aqueous acid, three alkenes, all with theformula C₉H₁₀, are formed.

 

i)​What are the structures of these three possible alkenes?

(2 marks)

 

ii)​State which one will be the major product and explain why.

(4 marks)

i.)PhCH=CH(CH₃) cis + trans; PhCH₂CH=CH₂

 

ii) Conjugation is a driver; trans isomer gives less steric clashes.

 

 

Previously, we discussed that the secondary alcohol shown below can be synthesised by reacting benzaldehyde (C₆H₅CHO) with methyl magnesium bromide (CH₃MgBr), followed by addition of aqueous acid.

 

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If this secondary alcohol is treated with NaCl, there is no reaction.

However if it is treated with HCl, it is converted to the correspondingchloroalkane, C₆H₅CHClCH₃.

 

Account for this difference in behaviour, in particular explaining why the substitution reaction has to be carried out in acidic conditions.

(4 marks)

•       The reaction may also be carried out using the acids, HCl, HBr and HI, but it will not work with a halide salt (e.g. NaCl) without the acid

•       The mechanism takes place via protonation of the OH group, which generates a more effective leaving group (H₂O rather than OH^-) in the subsequent substitution by the halide ion, X^-.

State the 2 ways in which ethers are produced?

• Dehydration of alcohols

• Williamson synthesis

Explain how the dehydration of alcohols forms ethers

• Ethers may be produced by losing 1 molecule of water between 2 molecules of an alcohol

Give a disadvantage of the dehydration of alcohols method for the synthesis of ethers

• Unreliable

• Gives a mixture of products depending on temp

Explain how the Williamson synthesis is used to prepare an ether

Sn2 mechanism between an alkoxide ion and an alkyl halide/sultanoate ester

Define an alkoxide ion

• Formed by the removal of a proton from an alcohol using a strong base

• OR reaction of the alcohol with sodium/potassium

• The R-O- is the ALKOXIDE ION

State the basic components in Williamson synthesis

• Alkoxide may be primary, secondary or tertiary

• Alkylating agent is primary

• Leaving group is a halide/sulfonate ester

Are ethers reactive or unreactive?

• Unreactive hence used a solvents

What are the 2 processes ethers undergo?

• Combustion

• Autoxidation via free radicals to produce a hydro peroxide

Define a hydroperoxide

• Compound containing the OOH group

Explain how a hydroperoxide is formed

• Ethers react with O2 at a C-H bond

• This is adjacent to the ether oxygen

• Via free radical mechanism

• 

What does substitution of ethers produce?

• haloalkanes

• Alcohols

What are the 2 reagents used in substitution of ethers?

• HI

• HBr

Why is HI the best reagent used in substitution?

• Very strong acid

• Iodide ion is a strong Nucleophile

Draw the mechanism for the substitution of ethers

What happens when aromatic ethers undergo substitution?

• One product is always a phenol

Draw the substitution mechanism for aromatic ethers

Define an epoxide

• The oxide of the alkene they are formed from

What happens in asymmetric epoxides?

• Nucleophilic attack occurs at the carbon atom in the 3 members ring

• Attack is at the C atom on the CH2

State and explain what crown ethers are

• Cyclic polyethers

• Have a -CH2CH2O unit

Why are crown ethers important?

• The cavity formed by the various oxygen atoms can complex to metal ions of different sizes

Give an application of crown ethers

• Purple benzene which has KMnO4 in benzene

• Normally it would not dissolve

• Crown ether creates a benzene soluble potassium ion

(a)       Identify which alkali metals chelate to the following crown ethers:

(a)       Draw a mechanism, with curly arrows, for the reaction between phenylethyl ether and hydrogen iodide.  (4 marks)

(a)  Draw a mechanism, with curly arrows, to show how diethyl ether is cleaved with two equivalents of hydrogen iodide.                                                                                                                                                                                              (7 marks)

(a)  Name two bases that can be used to deprotonate an alcohol in a Williamson ether synthesis.   (2 marks)

• removal of a proton from an alcohol using a strong base (NaH or NaNH₂)

• reaction of the alcohol with sodium or potassium.

(a)  Explain why, in terms of bonding and orbital overlap, epoxides are highly reactive.                                               (3 marks)

• Epoxides are both polarised and highly strained

• Overlap of the orbitals on neighbouring C and O atoms is partial

• This gives a weaker sigma bond

State 2 similarities between the C=C and C=O functional group

• Both contain double bonds

• Bond angles around carbon are 120 degrees

Give 1 difference between the C=C and C=O bond

• Nucleophiles attack the carbonyl carbon

Give 4 ways we can prepare aldehydes and ketones

• Oxidation of 1+2 alcohols

• Friedel crafts acylation of aromatic compounds

• Addition of water across alkyne triple bonds

• Treatment of acid chlorides with organocadium reagents

Draw the mechanism for friedel crafts acylation

Draw the mechanism for the addition of water across alkyne triple bonds

Explain the use of acid Chlorides with organicadium reagents for preparing aldehydes and ketones

• General formula of R2Cd

• Less reactive form of the organometallic compound

• Once the ketone has been formed from the acid chlorides there will be no further reaction

Give an example of nucleophilic addition with strong nucleophiles

• Grignard reagents (RMgBr)

• Cyanide ion (Cn-)

Give n example of nucleophilic addition with weak nucleophiles

• Water

• Alcohols

Give an example of nucleophilic addition with ammonia and it’s derivatives

• NH2X

• X can be H,OH,NH2

Draw the mechanism for the acid catalysed hydration of carbonyls

• Hydration occurs through nucleophilic addition

• With water or a hydroxide serving as a nucleophile

What is a formaldehyde and draw it

Draw the mechanism of nucleophilic addition with alcohols

What product does nucleophilic addition with alcohol form?

• Hemiacetal= if formed from an aldehyde

• Hemiketal= if formed from a ketone

Draw the mechanism for the formation of a hemiketal

Draw the mechanism for nucleophilic addition using NH3

1.    Draw a mechanism for the reaction of acetyl chloride (MeCOCl) with benzene. What is the organic product?

  In the presence of water and an acid catalyst, acetophenone will reversibly to form a hydrate. Outline, using “curly arrows”, the mechanism of this reaction:

 

          

As part of your answer, you should explain the role of the acid catalyst and why  it is necessary in this reaction.

 

 

• Hydrates are generally unstable, with the position of equilibrium lying far to the left.

• It has high electron density around the central carbon atom, which has four electron donating groups attached to it.

What type of bonding is present in carboxylic acids?

• Hydrogen bonding

• This is in water molecules and other acid molecules

How does the hydrolysis of nitriles aid in preparing a carboxylic acid?

What are the products of the hydrolysis of nitriles?

• Carboxylic acid

• Ammonia

What is a commercial source of a carboxylic acid?

• Acetic acid

How can acidity be increased of a carboxylic acid?

• Making RCO2- MORE STABLE

• Equilibrium shifts to the right

Which reactions of carboxylic acids form primary alcohols?

• Reduction

• With LiAlH4

State the order of reactivity for the derivatives of carboxylic acids

• Acid chlorides > anhydrides>esters> amides

• Become increasingly basic and nucleophilic across the series

• Thus less likely to act as leaving groups

• Lowers reactivity of the compounds

Name and draw the mechanism used to make carboxylic acids from acid anhydrides/acylation chlorides

• Nucleophilic addition elimination

• With H2O

Name and draw the mechanism used to form a primary amide from an acyl chloride/acid anhydride

• Nucleophilic addition elimination

• With NH3

Name and draw the mechanism used to form an ester from an acyl chloride/acid anhydride

• Nucleophilic addition elimination

• Alcohols eg-CH3OH

Name and draw a mechanism used to form an N-substituted amide from an acyl chloride/acid anhydride

• Nucleophilic addition elimination

• Amine eg- NHR

Draw what a general acid chloride structure is

Draw what a general acid anhydride structure is

• Loss of water between 2 carboxylic acid molecules

Why are amides less basic and less nucleopholic than related amines?

• The lone pair of electrons the N atom is partially delocalised into the neighbouring carbonyl group

• The C-N bond is stronger and shorter with a partial double bond character

Are amines less reactive than acid chlorides,acid anhydrides and esters?

• Yes because of the stability of the leaving group

What is a polyamide and how is it formed?

• Formed via the condensation rxn between the dicarbocylic acid and diamine

• This causes a loss of water between the 2 molecules

• Known as nylon

Draw and state how nylon-6 is formed?

• Polymerisation of 6-aminohexanoic acid

Define an amine and the 3 types of amines that are present

Explain hydrogen bonding in amines

• The N-H bond is polarised

• Lone pair of electrons on the N atom

Name and state the reagents used to produce a primary amine from a nitrile

• Reduction

• Using LiAlH4 in dry ether

Name and draw the mechanism used to form a primary amine form a halogenoalkane

• State the reagent

• Nucleophilic substitution

• With EXCESS NH3

State the equation for pKb

pKb= -logKb

What do lower values of pKb correspond to?

• Stronger bases

State the 3 factors controlling basicity

• Inductive effects of substituents

• Solvation effects

• Effects of delocalisation

Explain how inductive effects of substituents controls basicity

• Increasing the number of alkyl groups in the cations= increase in the basicity

Define solvation effects

• Water molecules surround the central positive charge

• Disperse it into lone pairs of electrons on the oxygen atoms

What is happening in this example?

• The more alkyl groups that are introduced

• Inductive effects increase

• Solvation effects decrease

Give 2 practical applications of protonation to give ammonium salts

• Isolation if naturally occurring alkaloids from plants

  • protonation gives a more water-soluble ammonium ion so they can be extracted into water

• Oral administration of medicines that are amines

Do amines act as nucleophiles?

YES to produce amides

State the equation for the reaction of amines with nitrous acid

• Acidification is conducted at ice temperatures

What can nitrosoamines be found in?

• Bacon

• Cigarette smoke

Draw the mechanism using SOCl2 to form haloalkanes from an alcohol

How is Hofmann degradation used to form amines?

• Forms a primary amine FROM a primary AMIDE

• Uses a strong base of NaOH

• In the presence of the halogenating agent Br2