Read for comprehension. In the next step of glycolysis, the C-1 aldehyde of glyceraldehyde 3-phosphate is converted into an acyl phosphate group. The energy from the oxidation of the C-1 carbon (from aldehyde to the carboxyl oxidation state) allows the formation of this high energy phosphate bond. The resulting 1,3-BPG has a high potential for phosphoryl group transfer. It is important to note that while the aldehyde is oxidized it is NAD+ which is reduced, to NADH. The loss of the hydride ion by the aldehyde moeity to NADH is similar to the haloform reaction except that instead of halide addition to the aldehyde leading to the tetrahedral intermediate, it is the sulfhydral group of a cysteine residue