Did you measure the resistor. 112ohm is not a standard value.
An Arduino pin can drive an IR LED through a >=100ohm resistor directly (~15mA average, ~30mA peak).
You only need a transistor if R= <= 100ohm.
IR LEDs have a Vf (working voltage) of ~1.2-1.5volt.
Two IR LEDs in series is twice the light for the same current draw.
Calculate the CL resistor accordingly.
Leo..