#ABSTRACTED implies absorption of the mind in something other than one's surroundings, and often suggests reflection on weighty matters. Thinking about his work with an abstracted smile, he did not really recognize or greet the people passing by.
#PREOCCUPIED often implies having one's attention so taken up by thoughts as to neglect others. Law students are often too preoccupied with their debts to focus on what really matters.
#ABSENT stresses inability to fix the mind on present concerns due more to mental wandering than to concentration on other matters. Students and employees are so naive that they pretend to pay attention in class or meetings with absent stares.
#ABSENTMINDED implies that the mind is fixed elsewhere and often refers to a habit of abstractedness. so absentminded, he's been known to wear mismatched shoes
#DISTRACTED may suggest an inability to concentrate caused by worry, sorrow, or anxiety. I was too distracted by grief to continue working.