Module 6 Flashcards
What evidence is there to reject the Kekulean model of benzene?
Relatively unreactive
- Benzene does not undergo electrophilic addition or decolourise bromine water as it would if there were double bonds
Carbon-carbon bond length
- X-ray diffraction has shown all of the bonds to be the same length (a length in between single and double)
Hydration Enthalpies
- The enthalpy of hydrogenation is less than 3x that of cyclohexene (which would be the expected value if Kekule was right)
Describe the structure of the delocalised model of benzene?
Adjacent p-orbitals overlap sideways to form a ring of electron density above the below the plane of bonding (known as a pi-system)
What reagents are required to nitrate benzene and what kind of reaction is it?
Electrophilic Substitution reaction, requiring nitric acid and sulphuric acid (to form NO2+ electrophile)
What reagents are required to halogenate benzene, and what kind of reaction is it?
Electrophilic substitution, requiring FeBr3 (to form Br+ electrophile), or the equivalent Fe-halogen compound
What reagents are required to alkylate benzene, and what kind of reaction is it?
Electrophilic substitution, requiring a haloalkane and a halogen carrier (e.g. FeCl3)
What reagents are required to acylate benzene, and what kind of reaction is it?
Electrophilic substitution, requiring an acyl-chloride and a halogen carrier (e.g. FeCl3)
What does phenol ‘behave as if it were’?
A weak acid, it can partially dissociate protons from its hydroxide group
How do you bromate phenol and what type of reaction is it?
Electrophilic substitution, add 3Br2, no catalyst is required
When phenol is nitrated (adding nitric acid), which 2 products are formed?
2-Nitrophenol and 4-Nitrophenol
Why is phenol more reactive than benzene?
The lone pair of electrons from the p-orbital of the OH is donated into the pi-system and makes the ring more electron dense, increasing susceptibility to electrophile attack
What effect(s) does the NH2 (anime) group have on the benzene ring?
It ‘activates’ it, allowing it to react more readily with electrophiles and also directing to positions 2 and 4 substitutions
What effect(s) does the NO2 (nitro) group have on the benzene ring?
It ‘deactivates’ it, making it less able to react with electrophiles and also directing to position 3 substitutions
What is the (general) relationship between?
All activating groups are 2 and 4 directing (except for halogens)
All deactivating groups are 3 directing
What are the alternate names of the 2,3 and 4 positon-substitutions?
2 is also known as ortho
3 is also known as meta
4 is also known as para
What are the conditions and reagents required for the oxidation of an aldehyde, and what does it form?
Potassium dichromate and sulphuric acid, under reflux, to produce butanoic acid
How can you reduce an aldehyde?
2[H] (from the NaBH4) and water, to produce a primary alcohol
How can you reduce a Ketone?
2[H] (from the NaBH4) and water, to produce a secondary alcohol
How can you form hydroxynitriles from a carbonyl compound?
Add sulphuric acid and sodium-cyanide (to form hydrogen cyanide in-situ) - good for increasing chain length
How can carbonyls react by nucleophilic addition with NaBH4, and how with NaCN?
Where an intermediate is formed and then protonated, making an alcohol or a hydroxynitrile respectively
How can you test for a carbonyl group?
Add Brady’s reagent (2,4-DNP in methanol and sulphuric acid), if positive, a yellow/orange ppt forms
How can you test for an aldehyde?
Add Tollen’s reagent, positive test forms silver mirror
How does the solubility of carboxylic acids change is the chain length increases?
Solubility decreases, because the effect of the hydrogen bond is ‘drowned out’ by the increasing alkane chain
How can you identify a carboxyl group?
By reacting it with a carbonate (they are the only common organic compound sufficiently acidic to react), a positive test will show effervescence
What is the name of the product (an ester) of the reaction between ethanoic acid and methanol?
Methylethanoate
How can you hydrolyse an ester bond?
- Acid hydrolysis under reflux, with water (reversible)
- Alkali hydrolysis under reflux, with OH- ions (irreversible), produces ethanoate ions
How can you form Acyl chlorides?
From carboxylic acid and SOCl2 (makes carboxyl-chloride and SO2 and HCl gas - so do it in a fume cupboard!)
What is produced when an acyl chloride reacts with an alcohol?
An ester
What is produced when an acyl chloride reacts with water?
A carboxylic acid
What is produced when an acyl chloride reacts with ammonia?
A 1” amide
What is produced when an acyl chloride reacts with a 1” amide?
A 2” amide
How could ethylamine act as a base?
Accept a proton to become an ethylammonium ion
How do you form a primary anime from a haloalkane?
Add excess NH3 then NaOH
How do you form a secondary anime from a haloalkane?
Add a primary anime then NaOH
How can you form an aromatic anime, from nitrobenzene?
6[H] and Sn + concentrated HCl and excess NaOH
What is a zwitterion?
An ion with no overall charge, since the charges of the groups behaving as an acid and a base both cancel out (at the isoelectric point)
How does a zwitterion behave at a pH higher than its isoelectric point?
As an acid, the inverse is true also
What is an optical Isomer?
Two versions of a molecule that cannot be superimposed, and are mirror images of one another
What types of polymers can be made from condensation?
Polyesters and polyamides
How can you hydrolyse polymers?
Acid (NaOH + H2O) or base (H+ + H2O) hydrolysis
How can you turn a haloalkane into a nitrile?
Add potassium cyanide
How can you turn a carbonyl into a hydroxynitrile?
add hydrogen cyanide (or make it in situ)
How can nitriles be reduced into animes?
Add H2 with a Ni catalyst
How can nitriles be hydrolysed?
Add water and HCl, under heat
How can you alkylate aromatic compounds?
Using a halogen carrier - AlCl3 etc. and a haloalkane
How can you acylate aromatic compounds?
Using a halogen carrier - AlCl3 etc. and an acyl chloride (to form an aromatic keytone)
How can you prepare an organic solid?
Reduced-pressure filtration, using a Buchner funnel and flask
Recrystallization, adding the hot-crystals to a solute and allowing it to cool out
How can you determine melting point?
Melting point apparatus
Thiele tube
What is a stationary phase (in chromatography)?
The phase that doesn’t move
What is a mobile phase (in chromatography)?
The phase that does move (through the stationary phase)
In gas chromatography, what is the stationary phase and what is the mobile phase, and how are the results presented?
Stationary Phase: Boiling Liquid
Mobile Phase: Carrier Gas (and sample mixture)
Output is ‘retention time’
