Chemistry · General Principles Of Organic Chemistry · NEET
They only tell you how far apart the two groups sit on the benzene ring. Ortho = the two groups are on adjacent (side-by-side) carbons, numbered 1 and 2. Meta = there is exactly one empty carbon between them, numbered 1 and 3. Para = the groups are directly across the ring from each other, numbered 1 and 4. Fix one group at carbon 1 and count to the second group to decide.
1,3 is meta. The trap is that 1,2 (neighbours) is ortho and 1,3 (one carbon gap) is meta. Easy rule: ortho starts with O and is the smallest gap, meta is the middle gap, para is the biggest gap. So the gap sizes go small-medium-large = ortho-meta-para = 1,2 / 1,3 / 1,4.
Because benzene has only 6 carbons in a ring, so the farthest a second group can be from carbon 1 is carbon 4 (three bonds away on either side). Positions 1,4 and going the long way 1,6-then-back give the same point directly opposite. We always use the lowest locant set, so it is written 1,4 (para), never 1,6.
Yes. For a disubstituted benzene you may write o- (ortho, 1,2), m- (meta, 1,3) or p- (para, 1,4) in front of the name, for example o-dichlorobenzene, m-dinitrobenzene, p-xylene. Modern IUPAC prefers the numbers (1,2- / 1,3- / 1,4-), but the o/m/p words are still used in NEET options and NCERT text.
No. The o-/m-/p- shorthand only works when there are exactly TWO substituents. With three or more groups you must use locant numbers (like 1,2,4-trimethylbenzene), because ortho/meta/para cannot describe three positions at once.
If one group sits on carbon 1, it has TWO ortho positions (carbons 2 and 6), TWO meta positions (carbons 3 and 5), and ONE para position (carbon 4). This matters in reactions: an ortho/para-directing group sends the next group to carbons 2, 4 or 6.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Ortho = 1,2 (next to each other), meta = 1,3 (one carbon apart), para = 1,4 (opposite ends) on a benzene ring.
o- = ortho, m- = meta, p- = para. They are placed before a disubstituted benzene name, e.g. p-nitrophenol means the two groups are 1,4.
The words are mainly used for a single benzene ring with two groups. For NEET, apply o/m/p to benzene; for other rings use locant numbers to be safe.
Because position changes properties. For example, o-nitrophenol has intramolecular hydrogen bonding (steam-volatile) while p-nitrophenol has intermolecular hydrogen bonding, so they separate and behave differently.
Position alone does not decide stability; it depends on the groups. Para often avoids steric crowding, while ortho groups sit close and can crowd or form internal H-bonds.
