Karteikarten
Benzene
Karten in diesem Stapel (15)
- 1Define aromatic compoundOne which contains a benzene ring
- 2What are the carbon-carbon bond lengths in benzene?All the bonds are the same length at an intermediate value between a double and a single C-C bond.
X-ray diffraction was used to measure the bond lengths - 3Define enthalpy of hydrogenation How can this be used to prove the modern day model of benzene compared to Kekule's cyclohexa-1,3,5-triene?The enthalpy change when 1 mole of an unsaturated compound reacts with an excess of hydrogen to become fully saturated.
When benzene is hydrogenated, the enthalpy change is 152 KJ mol-1 less than expected (compared to cyclohexa-1,3,5-triene). This means that actual structure is more stable - 4Define: sigma bond pi bond delocalised electronsFormed by direct overlap of 2 orbitals on adjacent carbons each providing 1 electron, so that the electron density is concentrated between the 2 nuclei (AKA covalent bonding).
Formed by the sideways overlap of 2 p orbitals on adjacent carbon atoms, each providing 1 electron.
Bonding electrons that are not fixed between 2 atoms, but shared by 3/more atoms. - 5What are the features of the delocalised model for benzene?-Planar hexagonal molecule (6 C atoms)
-All C-C bond lengths are intermediate in length between that of a single C-C and double C=C
-Each carbon uses 3 of its outer electrons to form 3 sigma bonds to C atoms and 1 H atom. 1 electron is left in the p orbital
-The lobes of the p orbital overlap sideways to form a ring of charge above/below the plane (produces a system of pi bonds) and delocalise. Produces region of electron density above/below ring.
-Delocalised p electrons make benzene more stable than theoretical compound cyclohexa-1,3,5-triene. Also accounts for intermediate C-C bond length
-120 degree bond angles - 6Define: substitution reaction addition reaction electrophile AcylationOne in which an atom/group of atoms is replaced with a different atom/group of atoms.
One in which a reactant is joined to an unsaturated molecule to make a saturated molecule.
An electron pair acceptor. It is an atom/group of atoms that is attracted to an electron rich centre where is accepts a pair of electrons to form a new covalent bond.
Process of replacing a hydrogen atom in certain molecules by an acyl group (RCO-) - 7Why is benzene resistant to addition reactions (so substitution reactions occur instead)? Is bromine water decolourised by benzene?-To undergo addition reactions, the electrons from the delocalised system in benzene would need to bond to the atom/group of atoms.
-This means the delocalised electron system would be broken, resulting in a loss of stability.
Bromine water is not decolourised by benzene as it does not undergo as addition reaction with bromine. - 8What is...called? C6H5 C6H5NH2 C6H5COCH3 C6H5CHCH2 C6H5OHPhenyl group
Phenylamine
Phenylethanone
Phenylethene
Phenol - 9What is the... in the nitration of benzene? electrophile conditions product(s) mechanism-NO2+ (nitronium ion)
-Conc nitric acid and conc sulfuric acid (catalyst) -forms nitrating mixture at 50 degrees Celsius
-nitrobenzene and water
-pg 239 - 10Why is conc sulfuric acid used? How is the nitronium ion formed?It is a stronger acid than nitric acid and will so donate a proton to it. Also it acts as a catalyst as it is regenerated when the H+ ion is released in the mechanism.
- 11Uses of nitration? (3)1) Manufacture of explosives eg TNT from nitrating methyl benzene. (A methyl group which is electron releasing make the benzene more susceptible to attack by electrophiles)
2) Formation of amines eg nitrobenzene can be reduced to Phenylamine.
3) In organic synthesis. - 12What is the... in the Friedel-Crafts reactions? electrophile conditions product(s) mechanism-CH3C+O (acylium ion)
-Aluminium chloride (catalyst), anhydrous (prevents hydrolysis)
-Phenylethanone and HCL
-pg 241 - 13How is the acylium ion formed? Equation?
- 14How is the reaction different if methyl benzene reacts with ethanoyl chloride in the presence of aluminium chloride?Reaction is faster since methyl group increases electron density of benzene ring which means electrophile is attracted more.
- 15Why is the Friedel-Crafts reaction important in synthesis of other organic compounds?Allows C-C bonds to form.
Acylation introduces a reactive carbonyl functional group to ring which can undergo reactions of a carbonyl group and act as an intermediate.
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- Beschreibung
- A2 Chemistry (Aromatic chemistry) Karteikarten am Benzene, erstellt von Dolu Falowo am 30/12/2016.
- Erstellt von
- Dolu Falowo · Dez 2016
- Aktualisiert
- 31 Dez 2016
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