Chemistry: Matter and Change

Chapter 9: Covalent Bonding

Problem of the Week

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/ch09_chapter.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a>
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0078664187/179001/ch9_1.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (18.0K)</a>Garlic and the Role of Phytochemicals
Phytochemicals are biologically active plant molecules often produced by plants to protect it from being damaged by bacteria, fungi and parasites. These naturally occurring plant chemicals are being demonstrated to help prevent chronic diseases, such as cancer and heart disease in humans.
Garlic, a perennial plant with white, starry flowers and bulb clusters of individual cloves, produces two important phytochemicals. For thousands of years, garlic has been used throughout the world as a medicine. Sanskrit records, from approximately 5000 years ago, describe the use of garlic remedies. Chinese, Egyptian, and Greek documents from Hippocrates, Aristotle and Pliny cite numerous therapeutic uses for garlic. In 1844 Theodor Wertheim, a German chemist, distilled a pungent substance from garlic and called it allyl, the Latin name for garlic. Four years later, Louis Pasteur in Paris showed that allyl could inhibit the growth of bacteria. This was a great discovery because 150 years ago, doctors had nothing to kill bacteria.
Whole garlic cloves are intact bulbs that contain an odorless, sulfur-containing amino acid derivative called ALLIIN, a covalently bonded compound with the chemical formula C6H11NO3S. When the bulb is crushed or cut, alliin is altered by the enzyme, alliinase and is converted into allicin. Allicin (C6H10OS2) is an oily, yellow liquid that gives garlic its characteristic odor. Modern research has confirmed that the garlic plant can be used to protect against infections, to lower blood cholesterol and fat levels, and to help with digestion.<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0078664187/179001/ch9_2.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (14.0K)</a>
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/POWproblem_1.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a>List the covalent bonds present in one molecule of allicin.
 
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/POWproblem_2.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Draw the Lewis structure for allicin.
 
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/POWproblem_3.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Using the bond dissociation energy table, determine the total bond energy for one molecule of allicin.
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0078664187/179001/ch9_3.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (12.0K)</a>Ajoene, C9H14OS3 an unsaturated sulfoxide disulfide, is the principal chemical responsible for garlic's anticoagulant properties. It is a component of allicin and is currently being developed as a pharmaceutical for the treatment of blood clotting disorders. As a naturally occurring "nutriceutical", this potent phytochemical might reduce the risk of stroke and heart disease. In addition, ajoene also has been found to have effective antimicrobial properties, inhibiting the growth of both bacteria and fungi.
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/POWproblem_4.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a>List the covalent bonds that are present in one molecule of ajoene.
 
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/POWproblem_5.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Draw the Lewis structure for ajoene.
 
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/POWproblem_6.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Using the bond dissociation energy table, determine the total bond energy of one molecule of ajoene.
 

Table: Bond dissociation energy (kJ/mol)

Bond
Energy
Bond
Energy
H-H
436
C=O
745
H-C
416
S=O
522
C-C
345
C=C
614
H-N
391
C-N
305
N-N
170
C≡C
839
H-O
464
C-O
358
O-O
138
C-S
259
H-F
569
O-O
145
F-F
159
C-F
488
H-Cl
431
O=O
494
Cl-Cl
243
C-Cl
330
H-Br
368
C-Br
288
Br-Br
192
N-N
170
H-I
297
C-I
238
I-I
151
N≡N
946
S-S
213
N=N
418
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/webLinks.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (1.0K)</a> Useful Web Sites:
Allicin - The Garlic Antibacterial
Allicin - The Smell of Health
Allicin in Garlic
Nova Online - Hot Science: Plant Magic
Table 6: Common Bond Energies and Bond Lengths
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