The structures of eight ( para-substituted benzaldehyde dialkylacetal)chromium tricarbonyl complexes [4-RC 6H 4CH (OR′) 2]Cr(CO) 3 (R = Me 2N, Cl, Me 3Si, CF 3; R′ = Me, Et) have been determined by single-crystal X-ray diffraction. For [4-Me 2NC,H 4CH(OMe) 2]Cr(CO) 3 ( 1), triclinic, P 1 , T = 291 K, a = 6.725 (2) Å, b = 7.228 (3) Å, c = 16.021 (8) Å, a, = 81.38 (4)°, β = 87.86 (3)°, γ = 87.77 (3)°, Z = 2; for [4-Me 2N C 6H 4CH(OEt) 2]Cr(CO) 3 ( 2), monoclinic, P2 1/ n, T = 123 K, a = 10.905 (7) Å, b = 15.670 (9) Å, c = 11.158 (9) Å, c = 116.61 (7)°, Z 4; for [4-ClC 6H 4CH(OMe) 2]Cr(CO) 3 ( 3), monoclinic, P2 1/ n, T = 293 K, a = 9.896 (3) Å, b = 12.872 (4) Å, c = 11.336 (4) Å, β = 108.21 (3)°, Z = 4; for [4-ClC 6H 4-CH(OEt) 2]Cr(CO) 3 ( 4), triclinic, p 1 , T = 293 K, a = 8.305 (3) Å, b = 9.999 (2) Å, a = 106.71 (2)°, β = 101.66 (3)°, γ = 110.27 (3)°, Z = 2; for [4-Me 3SiC 6H 4CH(OEt) 2]Cr(CO) 3 ( 5), triclinic, P 1 , T = 293 K, a = 6.933 (2) Å, b = 11.709 (3) Å, c = 12.071 (5) Å, a = 112.57 (3)°, β = 94.32 (3)°, γ = 100.52 (2)°, Z = 2; for [4-Me 3SiC 6H 4CH(OEt) 2]Cr(CO) 3 ( 6), monoclinic, P2 1/ c, T = 292 K, a = 11.823 (3) Å, b = 12.926 (4) Å, c = 14.608 (9) Å, β 113.03 (3)°, Z = 4; for [4-F 3CC 6H 4CH(OMe) 2]Cr(CO) 3 ( 7), monoclinic, P2 1/ n, T = 293 K, a = 6.756 (3) Å, b = 10.300 (3) Å, c 21.112 (6) Å, β = 95.18 (3)°, Z = 4; for [4-F 3CC 6H 4CH(OEt) 2]Cr(CO) 3 ( 8), monoclinic, C2/ c, T = 123 K, a = 18.992 (5) Å, b 14.065 (4) Å, c = 13.232 (4) Å, β = 110.53 (3)°, Z = 8. Compounds 1/ 2 exhibit an eclipsed carbonyl orientation, presumably owing to the presence of the strongly donating dimethylamino substituent. Compounds 3/ 4 exhibit a staggered arrangement, possibly reflecting electronic similarity between the chloro and acetal groups, or dominance of steric effects in conformation determination. Intriguingly, compounds 5/ 6 exhibit different geometries, as do 7/ 8, which by their nature do not appear to relate either to steric or electronic effects. It is proposed that more subtle factors, such as crystal packing forces, dictate the carbonyl orientation in these cases, suggesting that a priori prediction of the conformation is often unjustified.