Aromatic Chemistry Flashcards
What is the molecular formula of Benzene?
C6H6
Draw the Kekulé structure of Benzene?
Page 126 in text book
Explain why Kelulké’s structure is unusual and how it differs from an unsaturated alkene with an example.
Structure suggests benzene should react like an unsaturated alkene but instead it does not e.g.requires vigorous conditions and a catalyst whereas Alkenes react with aqueous bromine solution
True or false the evidence formed by keluké’s structure shows Benzene as being less reactive than an alkene? Explain answer.
True because it has no reaction with aqueous bromine solution unlike alkenes
What is the IUPAC name for Keluké’s structure?
Cyclohexa-1,3,5-triene
Explain why the enthalpy of hydrogenation proves that Benzene is more stable than cyclohexane-1,3,5-triene?
Cyclohexene has an enthalpy of hydrogenation (EH) of 119kjmol-1 therefore cyclohexane-1,3,5-triene predicts that the EH of Benzene would be -119 x 3=357.
However the EH of Benzene is 208kjmol-1 so Benzene is actually 149kjmol-1 more stable than cyclohexa-1,3,5-triene
What would you call the extra stability of Benzene in comparison to Cyclohexa-1,3,5-Triene
Delocalisation energy of Benzene
Benzene contains alternating C=C and C-C bonds? True or False?
False
How can the cyclic structure Benzene be confirmed?
X-ray diffraction
What are the Bond lengths in Benzene Alkene and Alkanes?
Benzene bond lengths is 0.140nm all around.
Alkene is 0.134nm
Alkane is 0.154nm
The fourth bonding electron is shared in a…
Pi Bond.
The ___ Bonds of the six ______ atoms overlap and the six ____________ atoms are shared in a d_________-shaped electron cloud above and below the _______ of the flat hexagon of carbon. The electrons in the pi bonds are said to be_______________ making Benzene more stable that Cyclohexa-1,3,5-triene.
Pi
Carbon
Doughnut
Plane
Delocalised
What group replaces hydrogen atoms on benzene when benzene undergoes nitrafication?
-NO2 replaces one of the hydrogen atoms
What ion is generated by mixing concentrated nitric acid and concentrated sulphuric acid and heating to 50 degrees?
Nitronium ion (NO2+)
What is produced when the concentrated sulfuric acid donates a proton to nitric acid .
An intermediate of [H2NO3]+ which
decomposes to yield the electrophillic nitronium ion ( you can see on page 129 text book)
In the Nitrafication of Benzene sulfuric acid also acts as a________ in the reaction.
A catalyst as it is regenerated when the HSO4- ion reacts with the H+ ion released in the last step it the reaction mechanism.
Nitro group can be reduced to…..
Amine group
What are the uses of Aromatic Amines?
Can be used in the dye industries or other industries
How can reduction be achieved for nitrobenzene?
Reduction can be achieved using iron, tin with conc hydrochloric acid or they can use catalytic hydrogenation with nickel and hydrogen gas
Explain what is meant by delocalisation of electrons in the benzene ring?
-Each carbon creates three covalent bonds
-Remaining electron is found in a p orbital T a right angle above and below carbon atom
-P orbitals overlap creating a ring of delocalised pi electrons above and below the structure
What type of covalent bonds are in benzene?
Sigma bonds
