Why benzene is so stable

Science · Chemistry · ages 20-21

Name ______________________ Date ____________

Benzene holds six pi electrons. Which whole number n makes 4n plus 2 equal 6?
Answer: ______________
Which list gives all four aromaticity tests?
- Closed loop, flat, conjugated, 4n plus 2 electrons
- Six atoms, flat, coloured, sweet smelling
- Closed loop, folded, alternating bonds, 4n electrons
Benzene prefers addition reactions because they keep its shared electron ring intact.
Circle one: True False
How does the nitrogen lone pair explain why pyridine is basic but pyrrole is barely basic?
- Both lone pairs join their pi counts, so both stay basic
- Pyridine has no lone pair on nitrogen at all
- The pyrrole lone pair joins the sextet and is tied up, while the pyridine lone pair stays free
The tropylium cation has seven atoms but only six pi electrons. Why is it unusually stable?
- Seven atoms always force stability on any ring
- It holds six pi electrons in a flat ring, meeting every test
- It has no pi electrons at all, so nothing can react
Cyclooctatetraene has eight pi electrons. Why is it nonaromatic rather than antiaromatic?
- It folds into a tub and is not flat, so it fails one test
- It holds 4n plus 2 electrons, which guarantees stability
- It has no double bonds, so there is nothing to count
A student claims pyridine is a weak base because its lone pair joins the aromatic count. What is wrong?
- Pyridine has no lone pair on its nitrogen atom
- Aromatic rings can never act as bases at all
- Its lone pair lies in the ring plane outside the pi count, so it stays free and basic
A student tests a flat conjugated five membered ring with four pi electrons and calls it aromatic. What is the error?
- Five membered rings can never be judged by any rule
- Four is a 4n count, so the flat ring would be antiaromatic, not aromatic
- Flat conjugated rings are always aromatic whatever they hold

Answer key

For grown-ups. Fold this page away before handing over the rest.

Why benzene is so stable W1-mt_2UmZKQozyN-s1

1 · With n equal to 1, 4n plus 2 gives 6, which is the benzene count.
Closed loop, flat, conjugated, 4n plus 2 electrons · All four tests must pass together: loop, flatness, conjugation, and the electron count.
False · Addition would destroy the ring, so benzene reacts by substitution instead.
The pyrrole lone pair joins the sextet and is tied up, while the pyridine lone pair stays free · A lone pair inside the aromatic count cannot also grab a proton, so pyrrole is barely basic.
It holds six pi electrons in a flat ring, meeting every test · Six pi electrons fit the rule with n equal to 1, so the cation earns aromatic stability.
It folds into a tub and is not flat, so it fails one test · Failing the flatness test takes the ring out of both categories and leaves it nonaromatic.
Its lone pair lies in the ring plane outside the pi count, so it stays free and basic · Only a p orbital lone pair joins the sextet, and the pyridine lone pair is not in one.
Four is a 4n count, so the flat ring would be antiaromatic, not aromatic · Four fits 4n with n equal to 1, and a flat conjugated 4n ring is destabilised, not stabilised.