Bonds that can break

Harmonic bonds cannot be broken and therefore molecular mechanics with harmonic approximation is unable to describe chemical reactions. When instead of harmonic oscillators we use Morse model (p. 169), then the bonds can be broken. 

And yet we most often use the harmonic oscillator approximation. Why There are a few reasons  

---

In contrast, aU the electrons in the compound on the right are localized. The lone-pair electrons on nitrogen caimot be shared with the adjacent carbon because carbon cannot form five bonds. The octet mle requires that second-row elements be surrounded by no more than eight electrons, so sp hybridized carbons cannot accept electrons. Because an sp hybridized carbon has a rr bond that can break, has a positive charge, or has an unpaired electron, it can accept electrons without violating the octet rule. 

Notice, as you study the following resonance contributors and practice drawing them, that electrons (tt electrons or lone pairs) are always moved toward an sp or sp atom. (Remember that an sp carbon is either a positively charged carbon or a double-bonded carbon and an sp carbon is generally a triple-bonded carbon Sections 1.8, 1.9, and 1.10). Electrons cannot be moved toward an sp carbon because an sp carbon has a complete octet and does not have a tt bond that can break, so it cannot accommodate any more electrons. 

The following species do not have delocalized electrons. Electrons cannot be moved toward an sp hybridized atom because an sp hybridized atom has a complete octet and it does not have a tt bond that can break, so it cannot accept any more electrons. 

Look again at Figure 16-1 If two NO2 molecules can form a bond when they collide, then that bond also can break apart when an N2 O4 molecule distorts. The concept of reversibility is a general principle that applies to all molecular processes. Every elementary reaction that goes in the forward direction can also go In the reverse direction. As a consequence of reversibility, we can write each step in a chemical mechanism using a double arrow to describe what happens at chemical equilibrium. 

These radicals decompose according to the /3-scission rule, which implies that the bond that will break is one position removed from the radical site, so that an olefin can form without a hydrogen shift. Thus the isopropyl radical gives propene and a H atom, while the //-propyl radical gives ethene and a methyl radical. The /3-scission rule states that when there is a choice between a CC single bond and a CH bond, the CC bond is normally the one that breaks because it is weaker than the CH bond. Even though there are six primary CH bonds in propane and these are somewhat more tightly bound than the two secondary ones, one finds substantially more ethene than propene as an intermediate in the oxidation process. The experimental results [12] shown in Fig. 3.12 verify this conclusion. The same experimental effort found the olefin trends shown in Table 3.2. Note that it is possible to estimate the order reported from the principles just described. 

The adsorption and ordering characteristics of the various hydrocarbon molecules on the low Miller index platinum surfaces are discussed in great detail elsewhere. These two surfaces appear to be excellent substrates for ordered chemisorption of hydrocarbons, which permit one to study the surface crystallography of these important organic molecules. The conspicuous absence of C-H and C-C bond breaking during the chemisorption of hydrocarbons below 500 K and at low adsorbate pressures (10 9-10-6 Torr) clearly indicates that these crystal faces are poor catalysts and lack the active sites that can break the important C-C and C-H chemical bonds with near zero activation energy. 

Termites can eat wood because they contain specific microorganisms that, in turn, contain bacteria that actually digest the wood. These bacteria have enzymes that can break the bonds of cellulose. 

High temperatures can break native S—S bonds and form new S—S bonds that can lock the protein into a denatured configuration. Low pH, sodium dodecyl sulfate. Tween 80 , chaotropic salts, and exogenous proteins have been used to protect proteins from thermal inactivation.f Ethylene glycol at 30-50% was used as a protectant of antiviral activity of p-interferon preparations. Human serum albumin was used inrecombinant human interferon-pser-i7, which resulted in increased thermal stability. Water-soluble polysaccharides such as dextrans and amylose and point-specific (site-directed) mutagenesis have also been used to increase thermal stability of therapeutic proteins and peptides. 

Without stratospheric ozone (O3), harmful solar radiation would cause gene alterations. Ozone forms when O2 breaks and each O atom reacts with another O2 molecule. It is destroyed by reaction with Cl atoms that are formed when the C—Cl bond in synthetic chemicals breaks. Find the wavelengths of light that can break the C—Cl bond and the bond in O2. 

---