ARENES

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  • Created by: Amira200
  • Created on: 03-06-16 22:22
What are arenas
Aromatic hydrocarbons containing one or more benzene rings
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Where do arenas occur from
Naturally in materials such as crude oil and coal
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What is benzene used for
A starting material for the synthesis of many aromatic materials such as phenol
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What is benzene
A six carbon hydrocarbon C6H6. It is colourless with a sweet odour but highly flammable
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What were the problems with Kekule's benzene structure
His model showed benzene had different bond lengths (3C-C3C=C) so benzene should have reacted like an alkene but it didn't. Enthalpy change hydrogenation more exothermic.Resistant to electrophilic attack.
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Describe the bonding and structure of a benzene molecule
P orbital overlap above and below ring forms a pie bond which is delocalised with a bond angle of 120. It is a planar ring
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Explain the relative resistance to bromination of benzene
Delocalised pie bond. Lower electron density. Induces a weaker dipole on Bromine. Polarises Bromine less.
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Explain the relative resistance to bromination of alkenes
Localised pie bond. Higher electron density. Polarises bromine more and induces a stronger dipole on bromine. no need for halogen carrier or high temp
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Explain the relative resistance to bromination of phenol
Lone pair of electrons on oxygen atom partially delocalised into benzene ring. Higher electron density. Polarises bromine more and induces a stronger dipole on bromine. Attracts electrophile more.
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What are the reagents and conditions for nitration of benzene
Concentrated nitric acid. Concentrated sulphuric acid. 50C/reflux
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What is nitrobenzene an important starting material for
Dyes, pharmaceuticals and pesticides
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What are the reagents and conditions for the bromination of benzene
AlBr3/FeBr3 catalyst.RTP
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Describe the relative solubility of phenol
It is slightly soluble in water because the OH group can form hydrogen bonds in water. The presence of a benzene ring is what makes phenol less soluble than alcohols
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What 3 reagents does phenol react with
Na, NaOH, Br2
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What is the name of the product when phenol reacts with 3 bromines and what is the second product
2,4,6-tribromo phenol. HBr
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What are the uses of phenol
Antiseptics. Disinfectants.Resins for paints.Detergents. Pharmaceutical products
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How can you oxidise a primary alcohol into a carboxylic acid
Heat under reflux with acidified potassium dichromate
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What do you need to do if you only want to obtain an aldehyde from the primary alcohol
Distill mixture immediately to prevent further reaction into COOH
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How do you turn an aldehyde or ketone back into its alcohol
React with NaBH4
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What is the name of the mechanism when a carbonyl compound (Aldehyde or ketone) returns back into its original alcohol
Nucleophilic addition
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What is happening to the aldehyde or ketone to make it turn back into its alcohol
It is being reduced
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What observation can be made with acidified potassium dichromate
When a compound has been oxidised a colour change from orange to green will be present
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What reaction can be carried out to detect a carbonyl compound
Bradys reagent.(2 DNPH methanol and sulphuric acid) Aldehyde and ketone will form orange ppt.
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How can you distinguish between an aldehyde and ketone
Tollens reagent (Ammoniacal silver nitrate) Aldehyde will show silver mirror as it is oxidised into a carboxylic acid. The ketone will not react so will show no change as it cannot react any further
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How do you identify the carbonyl compound
Purify and recrystallise impure sample. Measure and record melting point. Compare with known values
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Why is it easier to identify a carbonyl compound in its 2,4-DNPH form rather than their original form
Because in their original form their boiling points are ver similar whereas in their 2,4DNPH version their melting points are many degrees apart
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Explain the relative solubility of carboxylic acids
COOH are soluble in water as their O atom from OH group forms hydrogen bonds with water (the H in water)
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What 3 reactants do carboxylic acids react with and what do they form
Metals and metal hydroxides forming carboxylate salts and hydrogen/water. Metal carboxlates forming carboxylate salt, water and carbon dioxide
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State the uses of esters
Perfumes and flavourings
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Which two ways are used to produce esters
Alcohol + COOH = ester + water. Alcohol + acid anhydride = Ester + COOH
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What are the reagents and conditions for esterification
Concentrated sulphuric acid under reflux
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State the reaction of acid hydrolysis of esters
Ester + water + HCl = COOH + alcohol.
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State the reaction of base hydrolysis of esters
Ester + NaOH + reflux = carboxylate salt + alcohol
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What is the systematic name of glycerol
1,2,3-tribromopropane
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How is a triglyceride formed
Adding a fatty acid to glycerol
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What are fatty acids
Long chain hydrocarbons with a carboxylic acid at the end
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What is the difference between a saturated fatty acid and an unsaturated fatty acid
Saturated means single bonds only whereas unsaturated has a C=C double bond
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What is the name of the reaction when forming a triglyceride
Condensation reaction as (3) ester bonds are forming
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What are the good fatty acid and why are they good
Cis fatty acids are good as they are thought to increase the amounts of HDLs in the blood and encourage more LDL's to leave the blood and be excreted. They exist as liquids at room temperature as the fatty acid chains don't pack closely togetho
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What are the bad fatty acids and why are they bad
Trans saturated fatty acids are bad because they increases the amount of LDL's returning back into the blood when they are supposed to be excreted increasing chances of heart disease. The fatty acids are packed closely together making them solid at r
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Why is biodiesel being favoured more recently
It is a renewable source of fuel compared to non renewable fossil fuels.
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How is biodiesel produced
Using waste cooking oil as a source of fatty acids and reacting with methanol or ethanol along with a KOH catalyst to produce biodiesel and a methyl/ethyl ester
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What is the formula for biodiesel
3(CH3OCOR)
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What are advantages and disadvantages of using biodiesel.
Carbon neutral, improve atom economy. However feasibility issues to do with poor farmers using crop land for planting biodiesel for more money instead. May have to convert engine so can accept 100% biodiesel
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Explain the basicity of amines
They act as a base accepting a proton as they have a lone pair of electrons on their nitrogen atom
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How do amines form a salt
By reacting with an acid to form a dative covalent bond
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How do you prepare a primary aliphatic amine
Add excess ammonia to a halogenoalkane with ethanol as a solvent. Heat gently to form an aliphatic amine and HX
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Why is excess ammonia required
To minimise further substitution
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How do you convert nitrobenzene into phenyl amine
Sn catalyst. Conc HCl. 6[H]. It will make water also as a second product
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What are the names of the two steps involved in the synthesis from phenyl amine
1) Diazotisation 2)Coupling reaction
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What are the uses of the reaction from phenyl amine
Dyes
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Describe the diazotisation process
NaNO2 + 2HCl makes HNO2 + NaCl.
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Describe coupling reaction
Add NaOH + phenol under alkaline conditions and
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Card 2

Front

Where do arenas occur from

Back

Naturally in materials such as crude oil and coal

Card 3

Front

What is benzene used for

Back

Preview of the front of card 3

Card 4

Front

What is benzene

Back

Preview of the front of card 4

Card 5

Front

What were the problems with Kekule's benzene structure

Back

Preview of the front of card 5
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