Once, I had read a piece of information about the phrase "ought to" which implied that I can leave out "to" when it comes in the negative & interrogative form. For example:
She oughtn't (to) have bought bread for lunch. We already had some.
Is that piece of information correct or not?
Thanks in advance.
In your example, no, you need the 'to' infinitive, just as you would in a normal infinitive construction.
She ought to have brought bread.
She ought not to have brought bread.
(It may help you not to use the contracted form.)
However I can think of contexts in which omitting the 'to' is acceptable, and probably preferable.
She ought to run to catch the bus.
She oughtn't run to catch the bus.
I presume (and I don't know for sure), that this practice has arisen due to how the synonymous 'should' is used in English.
She should run to catch the bus.
She shouldn't run to catch the bus.
However, using 'ought' in the second example, would be considered quite unusual and probably archaic. In both cases 'should/shouldn't' is probably easier to use, and 'ought' would not be expected in general conversation.
Looking at the Cambridge Dictionary, I believe the 'to' should always be present in the negative form, however it is sometimes omitted in ways that sounds natural to an English speaker. In other words, you are probably safer always including the 'to', than guessing when you can omit the 'to' and possibly getting it wrong.
Better still, just say 'should/shouldn't'.
