Hydrogen bond oxygen atom

Protein chains (Figure 23.8) can align themselves so that certain patterns are repeated. These repeating patterns establish what we call the secondary structure of the protein. The nature of the pattern is determined in large part by hydrogen bonding. Oxygen atoms on C=0... 

Fig. 19.2. Structural diagram for polywater consisting of a network of hexagonal units. This structure, as drawn, would have a negative charge. An appropriate number of hydronium ions, protons, or tetra-coordinated hydrogen-bonded oxygen atoms would be required to maintain the empirical formula (HjO),. (Lippincott et aU 1969.)...

Fio. 16. Diagram showing the relative positions in a crystal of acetamide of an acetamide molecule and the hydrogen-bonded oxygen atoms of two adjacent molecules. 

Fig. 10. Pharmacophores for angiotension-converting enzyme. Distances in nm. (a) The stmcture of a semirigid inhibitor and distances between essential atoms from which one pharmacophore was derived (79). (b) In another pharmacophore, atom 1 is a potential zinc ligand (sulfhydryl or carboxylate oxygen), atom 2 is a neutral hydrogen bond acceptor, atom 3 is an anion (deprotonated sulfur or charged oxygen), atom 4 indicates the direction of a hydrogen bond to atom two, and atom 5 is the central atom of a carboxylate, sulfate, or phosphate of which atom 3 is an oxygen, or atom 5 is an unsaturated carbon when atom 3 is a deprotonated sulfur. The angle 1- -2- -3- -4 is —135 to —180° or 135 to 180°, and 1- -2- -3- -5 is —90 to 90°.

We have now discussed three types of intermolecular forces dispersion forces, dipole forces, and hydrogen bonds. You should bear in mind that all these forces are relatively weak compared with ordinary covalent bonds. Consider, for example, the situation in HzO. The total intermolecular attractive energy in ice is about 50 kj/mol. In contrast, to dissociate one mole of water vapor into atoms requires the absorption of928 kj of energy, that is, 2(OH bond energy). This explains why it is a lot easier to boil water than to decompose it into the elements. Even at a temperature of 1000°C and 1 atm, only about one H20 molecule in a billion decomposes to hydrogen and oxygen atoms. 

Collagen forms a triple helix, where three chains of connected amino acids form weak hydrogen bonds between the double-bonded oxygen atoms and the hydrogen atoms attached to the adjacent chain s nitrogens. The three chains then twist together like three cords in a rope. 

Imagine that this reaction occurs along a two-step path. In the first step, the bonds In the reactants break, yielding four hydrogen atoms and two oxygen atoms. In the second step, the hydrogen and oxygen atoms form two water molecules that contain four O—H bonds. 

Water, however, is a wonderful solvent for ionic-bonded substances such as salt. The secret to its success lies in the electric dipoles created by the polar covalent bonds between the hydrogen and oxygen atoms. In water, the polar bonds are asymmetric. The hydrogen side is positive the oxygen side is negative. One measure of the amount of charge separation in a molecule is its dielectric constant. Water has a dielectric constant that is considerably higher than that of any other common liquid. 

Where s = sin cc/2, c — cos ajl (with a the equilibrium bond angle) and r is the equilibrium O-H bond length, as shown in Fig. 3. The masses of the hydrogen and oxygen atoms are arranged according to Eq. (42) in the order established by the vector f namely,... 

Draw an electron dot diagram for HNO . Note Double-bonded oxygen atoms do not bond hydrogen atoms as a rule. 

The hydrogen is bonded to the single-bonded oxygen atom. 

We see the possibility of a substance having several types of bond. Consider water for example. Formal covalent bonds hold together the hydrogen and oxygen atoms, but the individual water molecules cohere by means of hydrogen bonds. Conversely, paraffin wax ( /7-C15H32) is a solid. Each carbon is bonded covalently... 

We can represent groups of atoms or ions by models. For example, to hold two ping-pong balls together they must be stuck or connected by a rod. There likewise must be a connection between the sodium and chloride ions in table salt or between the hydrogen and oxygen atoms in water. This force of attraction that holds atoms or ions together is called a chemical bond. 

Total spatial-energy action upon the bond H-O-H of magnesium and nitrogen atoms (table 3) results in the possibility of breaking this bond with the isolation of free hydrogen and oxygen atoms. 

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