9701 · 29.3
Shapes of aromatic organic molecules; σ and π bonds — FAQ
Frequently asked questions for 9701 Shapes of aromatic organic molecules; σ and π bonds. Direct answers first, then deeper explanation — then practise with marking.
Is benzene the same as cyclohexa-1,3,5-triene?
No. Cyclohexa-1,3,5-triene is a hypothetical molecule with alternating, distinct single and double bonds of different lengths. Benzene is a real molecule where all C-C bonds are identical in length and strength due to a delocalised π system, which makes it significantly more stable.
Why is the bond angle in benzene exactly 120°?
Each carbon atom is sp² hybridised, forming three σ bonds. According to VSEPR theory, three regions of electron density around a central atom will arrange themselves to be as far apart as possible, resulting in a trigonal planar geometry with 120° bond angles.
If benzene is so stable, why does it react at all?
While the aromatic ring is very stable, the delocalised π system is a region of high electron density. This makes it susceptible to attack by strong electrophiles (electron-seeking species). The reactions proceed via a substitution mechanism that allows the stable aromatic ring to be regenerated in the final product.
What does the circle inside the hexagon represent when drawing benzene?
The circle represents the six delocalised π electrons that are shared equally among all six carbon atoms in the ring. It is a more accurate representation of benzene's bonding than the Kekulé structure with alternating double bonds.