Aromatic chemistry Flashcards
what is benzene
a colorless sweet smelling highly flammable liquid
found naturally in crude oi, is a component of petrol and also found in cigarette smoke
classified as a carcinogen that is it ca cause cancer
what is benzene classified as
aromatic hydrocarbon
what is the molecular formula of benzene
C6H6
what is the KeKule model
suggested that the structure of benzene was based on a six membered ring of carbon atoms joined by an alternate single and double bonds
what evidence is there to disprove Kekule’s model
1)the lack of reactivity of benzene
2)the lengths of the carbon-carbon bonds in benzene
3)hydrogenation enthalpies
why are benzene rings unreactive
contains C=C double bond. It should decolorize bromine in an electrophilic addition reaction. But
-benzene does not undergo electrophilic addition reactions
-Benzene does not decolorizes bromine under normal conditions
Led to scientist to believe that benzene cannot have a C=C bond
how does the length of carbon -carbon bonds in benzene disprove K’s model
X-ray diffraction possible to measure bond length in a molecule
.-when benzene was examined all the bonds in benzene bond were 0.139nm in length
-this bond length was between length of a single bond 0.153 and double bond 0.134
how does hydrogenation enthalpies disprove K’s model
if benzene did have the Kekule structure , then it would be expected to have an enthalpy change of hydrogenation that is three times that of cyclohexane. When cyclohexane is hydrogenated one double bond reacts with hydrogen. The enthalpy change of hydrogenation -120Kj
What is the expected for the mentally change for reacting 3 double bonds with hydrogen
3 x -120 = -360
What is the actual enthalpy change of enthalpy change of hydrogenation of enthalpy
The actual enthalpy change of hydrogenation of benzene is only
- 208k/mol-. This means that 152.kJmol’ less energy is produced than expected.
what led to scientists to lead to propose the delocalized model
The actual structure of benzene is therefore more stable than the theoretical Kekulé model of benzene.
what is the empirical formula for benzene
CH
what is the basic model of the delocalised model of benzene
Benzene is a planar, cyclic, hexagonal hydrocarbon containing six carbon atoms and six hydrogen atoms
Each carbon atom uses three of its available four electron in bonding to two other carbon atoms and to one hydrogen atom
What is the model of delocalised model of benzene regarding orbitals
-Each carbon atom, has one electron in a p orbital at right angles to the plane of the bonded carbon atom and hydrogen atoms
-Adjacent p-orbital overlaps sideway in both directions above and below the plane of the carbon atoms to form a ring of electron density
-This overlapping of the p orbital creates a system of pi bonds which spread over all six carbon atoms in the ring structure
-The six electron occupying this system of the pi bond are said to be delocalized
what are compounds with one substituent group called
monosubstituted
