Many English words are negatives whose opposites are either obolete or very rare. These negatives often have prefixes such as -dis, -in and -un. Here is a list of words without pairs:
The word unkempt comes from the Old English word kemb, which means comb. It used to mean uncombed but now means neglected.
The word ruly was once common and meant law-abiding. It is now very rare. To be reckless is to be unconcerned about the consequences of an action. The opposite doesn't exist.
The word nonchalant can be defined as indifferent and unconcerned. The opposite doesn't exist. The opposite of innocent is guilty; nocent is rarely used.
English has a number of words which don't have antonym pairs. These words are negatives whose antonyms are either no longer used or have become very rare. It appears that the negative of an antonym pair is more likely to survive than the positive.