We explore general properties of the main peak of the structure factor S(q) near the melting temperature T melt in liquids confined in two dimensions, especially for the one component plasma model and for monatomic liquids interacting through inverse twelfth-power potentials. Those properties are the height of the peak, S(q m), where q m is the position of maximum in the peak, and the ratio between S(q m) and q m/Δq, where 2Δq is the width of the peak. The results obtained are then compared with those for similar systems in three dimensions. Other magnitude that we use to compare two-dimensional and three-dimensional simple liquids is r m/Δr, where r m is the position of the main peak in the pair distribution function g(r) and 2Δr is the width of that peak.