Compare the two sentences given below.
I went to his office to meet him.
I went to his office in order to meet him.
Although the second sentence is technically correct, it sounds too formal and is usually avoided.
Both to + infinitive and in order to + infinitive express the same meaning when expressing purpose.
She worked hard to pass.
She worked hard in order to pass.
To reach him, I had to wait for five minutes on the line.
In order to reach him, I had to wait for five minutes on the line.
Before a negative infinitive, we usually prefer in order to.
In order not to miss the train, I started early. (More natural than ‘Not to miss the train, I started early.’)
Note the position of ‘not’ in the structure. It goes before to.
In order not to wake up the baby, I tiptoed into the room.
The expression so as to can also be used to express purpose. It carries the same degree of formality as in order to.
I am planning to move house so as to be closer to my place of work.
I am planning to move house in order to be closer to my place of work.
Before stative verbs (e.g. seem, appear, know, understand, have), we normally use so as to or in order to.
I talked to him so as to have a better understanding of the situation.
I asked her out in order to know whether she had any interest in me.