Can you tell just by looking at an alkyl halide whether or not it will undergo E1 or E2 subsitution?

E1 - Elimination unimolecular ( i guess )... So basically it is a 2 step process... This is only possible with a tertiary or secondary alkyl halide... Im guessing you are in year 12 and just started organic HL content.... E2 - similar to Sn2 = BACK SIDE attack (yep, you can go around my school and say Sn2 and even the people who dont take chemistry know what it means) Back side attack is only possible in primary compounds because of the free space on the left of the center carbon, where only a hydrogen particle awaits to be "attacked" .... So yep the type of molecule gives it away.... When a carbon atom is "bonded" to 1 other carbon friends, its a Primary, when its bonded to 2 other carbon friends, its secondary and if its really social and bonded to 3 carbon atoms, its a Tertiary... Its all about probability... its always possible for a primary to undergo E1, however the probability is low, hence we assume that it doesn't happen. If you want a good book for IB Chemistry, i would recommend Talbot :)