Phase transitions temperatures and temperature dependence of helical pitch p for S-(+)-4 '-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[(4,4,4,3,3,2,2-heptafluorobutoxy)alkoxy] benzoates, and 3-fluoro-, and 2-fluoro-, 2,3-difluoro-benzoates upon length of alkoxy spacer were tested. For etoxy and propoxy spacer the pitch p in antiferroelectric phase is increasing with temperature to maximal value of about 1000nm in high temperatures region. For pentoxy, hexoxy, and heptoxy spacer the pitch p is longer and reverse temperature dependence is observed. The compounds convenient for formulation of antiferroelectric orthoconic mixture with pitch length of about 2000nm were selected.