Aspirin molecular structure

Figure 9.1.3 The molecular structure of aspirin or acetylsalicylic acid.

Figure 13.4.4 The molecular structure of aspirin, acetylsalicylic acid.

FIGURE 7.32 The molecular structures of some analgesics (a) aspirin (b) acetaminophen and (c) morphine. Note how slight the differences are among morphine, codeine, and heroin. 

Late in the last century, a beginning was made in the task of simplifying the molecular structure of natural products while retaining the therapeutic action. It was hoped in this way to obtain substances which coiild be more easily synthesized and which might be free from toxic side effects introduced by unwanted parts of the molecule. The introduction of salicylic acid into medicine in 1875 was one of the earliest results of this endeavour, and this acid and its salts and derivatives such as aspirin replaced the use of willow bark, and the glucoside of salicyl alcohol which this bark contained. 

FIGURE 6.18 (a) Molecular structure of the (100) surface of aspirin, (b) Molecular structure of the (002) surface of aspirin. 

The Crystal and Molecular Structure of the g-Cyclodextrin Inclusion Complex with Aspirin and Salicylic Acid... 

Fig. 1 (a),(b) The structure of 3 CyD aspirin complex (1) and (2), viewed from the primary hydroxyl side of each 3-CyD, respectively, (c) The molecular structure of (3 CyD)2(aspirin)2 salicylic acid complex. Aspirin and salicylic acid are drawn by full lines and circles. One of the statistically disordered salicylic acid at three sites is shown in the center of 3-CyD dimer. 

M Figure 1.24 (a) A molecular model of aspirin, the highlighted portion of the molecule is transferred when aspirin deactivates the COX-2 enzyme, (b) Molecular model of a potential new "super-aspirin" whose molecular structure is related to that of aspirin. 

One of the best ways to grow new polymorphs of a given substance is by diversifying crystallization experiments. Several examples wherein attempted co-crystallization of two compounds resulted in the serendipitous crystallization of a new polymorph of one of the components have been reported in the recent literature. New polymorphs of aspirin and maleic acid, ° trinitrobenzene, and four polymorphs of benzidine " were unexpectedly obtained during attempted co-crystallization experiments. In contrast to the well-understood role of structurally related tailor-made additives, the selective growth of a particular polymorph during attempted co-crystallization experiments is difficult to explain because the components have different molecular structures and complementary functional groups. However, the technique has shown early promise in the discovery... 

Several analyses have been devoted to studies of compounds which are commonly used as complexing agents, usually in an attempt to define those features of the molecular structures which may be of relevance to complex-forming properties. Thus 2-oxazolidinone (1) forms a wide variety of complexes with compounds such as phenols, aspirin, saccharin, and iodine. The conformation proves to be planar, and the molecular dimensions [C(l)-N 1.301(8) A, C(l)-0(1) 1.210(8) A, C(l)-0(2) 1.356(10) A] are said to indicate that (lb) and (Ic) are major resonance components. On this basis, 2-oxazolidinone possesses a highly polarized molecular structure, and this feature may well explain the unusual complexing properties. 

Figure 5.3 (a) Ball and stick representation of aspirin, (b) Ribbon representation of dihydrofolate reductase, (c) Mesh representation of aspirin. This representation shown simultaneously both the space fill and stick structures of the molecule, (d) Molecular dynamics representation of aspirin at 500 K. The relative movement of the atoms with time within the molecule is indicated by the use of multiple lines between the atoms... 

The vital importance of size and shape as compared with absolute molecular weight is emphasized by another pair of exceptions on the calibration curve in Figure 5-37—aspirin and propylparaben. These two compounds have essentially identical molecular weights (180.2 and 180.1, respectively), but are easily separated by SMGPC. From the structures, it can be deduced that propylparaben acts as a larger molecule in solution than does aspirin. This is probably due to a solvent effect where the THF hydrogen-bonds to the polar groups in propylparaben. Thus, propylparaben should elute before aspirin, and as shown on the calibration curve, it does. 

Small differences in the structure of the molecules result in changes in the elution volumes. Note the difference that shortening the side chain from propyl to methyl has on the elution volume of the paraben. Even such a minor difference is sufficient to permit the separation of these two compounds. The same effect can be observed if aspirin (acetylsalicylic acid) is hydrolyzed to salicylic acid. Reduction in molecular size increases the elution volume. 

One example that illustrates this is the GPC separation of aspirin and propyl paraben. These two compounds have identical molecular weights (MW = 180) but can be separated using GPC (e.g., on a 100-A jiStyragel columns). From the structures (Fig. 11-3) it can be hypothesized that propyl paraben acts as a larger molecule in solution than does aspirin. Since the side chain on propyl paraben would give the molecules a larger end-to-end size than the more compact aspirin molecule, propyl paraben should elute before aspirin. 

Molecular formulas give information only about what makes up a compound. The molecular formula for aspirin is C9H8O4. Additional information can be shown by using different models, such as the ones for aspirin shown in Figure 17. A structural formula shows how the atoms are connected, but the two-dimensional model does not show the molecule s true shape. The distances between atoms and the angles between them are more realistic in a three-dimensional ball-and-stick model. However, a space-filling model attempts to represent the actual sizes of the atoms and not just their relative positions. A hand-held model can provide even more information than models shown on the flat surface of the page. 

Molecular model and structure of aspirin. The analgesic action is thought to arise because aspirin interferes with the synthesis of prostaglandins, which are hormones involved in the transmission of pain signals. 

The molecular formula for aspirin is CsHbOi,. Its structure is shown below. 

Compare the molecular weight of aspirin as calculated from your experimental data with the molecular weight as calculated from the molecular formula. Explain the difference. Draw structures if necessary. 

A) Structure of the drug sulfadimidine 9 and (B) hydrogen-bonded molecular complex between sulfadimidine and acetylsalicylic acid (aspirin) in the co-crystal. 

---