as of may 2009 unless there has been a change , i retired from C90 in june here are the 5 vector freqs.
west arr/133.62 ,east arr/119.0, center arr/125.7, east trip/135.02 east feed/124.35.Center arrival freq only used when ORD is on West Flow rwys 27R/27L/28.any other time ORD is on 3 rwys east trip / east feeder is the freq used example rwy 4R/10/9R, 22R/27L/28, .most of the time the trip final is on 124.35 and not on the east trip freq, the 2 primary vector freqs will be east/west arrival with the others used as needed.also when ORD is on 22R/14R/10 than the rwy 10 vector freq is 135.07 which is west feeder.
OG