Porphine 3D Download 3D Porphine contains four pyrrole molecules which have been joined to form a larger ring system. This molecule has 18 p electrons in the ring system, and is therefore aromatic. Like other aromatic molecules, this ring system is especially stable.
The ring system is flat, since all of the carbon and nitrogen atoms in the ring are sp 2 -hybridized, and therefore trigonal planar in shape.
This leaves the molecule with a large open cavity in the center, with four nitrogen atoms pointing towards the center of the cavity. Porphine is the parent compound of a class of molecules called the porphyrins , in which various substituents replace the hydrogen atoms on the outside of the porphine ring. The name "porphyrin" is derived from the fact that many of these substances form purple crystalline solids the Greek word for "purple" is "porphyros". Porphyrins occur ubiquitously in nature, especially in systems involving respiration see Heme and Chlorophyll below.
The protein hemoglobin contains four subunits two "alpha" and two "beta" subunits , each of which complex a heme molecule; this protein is responsible for oxygen transport in the body. The iron atom in heme forms complexes with oxygen molecules, which are carried throughout the body by the hemoglobin in the red blood cells. Chlorophyll 3D Chlorophyll Greek, chloros "green" and phyllon "leaf" is a porphyrin derivative found in green plants and cyanobacteria which allows these organisms to perform photosynthesis.
Shown below are the structures of chlorophyll a and chlorophyll b ; the magnesium-free forms of these molecules are called pheophytin a and pheophytin b. The three-dimensional structure shown on the right is that of pheophytin a. A double bond in one of the pyrrole rings in the porphyrin macrocycle is reduced to a single bond in the structure below, this is the carbon-carbon bond to which the long side-chain, sometimes called the phytyl group, is attached ; these "dihydroporphyrins" are known as chlorins.
The energy from the sunlight that is absorbed by chlorophyll in the chloroplasts of green plants is used to drive the synthesis of carbohydrates such as glucose C 6 H 12 O 6 from carbon dioxide and water:. This equation summarizes a lot of complex chemistry, which it is beyond the scope of this page to try to summarize.
In the fall, the green color of many plants disappears as the chlorophyll starts to break down; this allows other pigments, such as carotenes, in the leaves to "show their colors," producing the vivid yellows and oranges associated with fall colors.
Buckminsterfullerene , or C 60 , is a soccer-ball shaped molecule consisting of 60 carbon atoms. The molecule was discovered by H. Kroto, R. Smalley, and R. Curl in the s in experiments involving graphite vaporized with lasers they were awarded the Nobel Prize in Chemistry for their discovery in The structure, a truncated icosahedron, having 12 pentagons and 20 hexagons, reminded them of the shape of the geodesic dome designed by the architect R.
Buckminster Fuller, and they named the molecule in his honor. Similar spherical-shaped carbon-only molecules, such as C 70 , are often referred to as fullerenes or "buckyballs. The fullerenes are considered another allotrope stable structural form of carbon, in addition to graphite and diamond. In the s it was discovered that C 60 could be made in larger quantities by heating graphite in an inert atmosphere.
Since then, these molecules have been intensely investigated. Nanotubes are cylindrical versions of the fullerenes; they look something like a chain link fence rolled into a cylinder, with a dome-shaped cap on the end half of a buckyball. Nanotubes also known as "buckytubes" are extremely strong, as well as being very lightweight since they are made of nothing but carbon atoms. These materials are being tested for potential use in many materials; some nanotubes also conduct electricity, leading to some potential applications in circuit design and electronics.
C 70 3D Download 3D C 70 is another example of a fullerene. It has a slightly elongated, oval shape. Atkins, Molecules , 2nd ed. Cambridge: Cambridge University Press, , p. Paula Yurkanis Bruice, Organic Chemistry , 4th ed. Upper Saddle River: Prentice Hall, , p. Marye Anne Fox and James K. Whitesell, Organic Chemistry , 3rd ed. Sudbury: Jones and Bartlett Publishers, p. Maitland Jones, Jr. New York: W. Richard J. Lewis, Sr. New York: Van Nostrand Reinhold, Englewood Cliffs: Prentice Hall, , p.
Royston M. Roberts, Serendipity: Accidental Discoveries in Science. Sharp, The Penguin Dictionary of Chemistry , 2nd ed. London: Penguin Books, Wade, Jr. Martha Windholz ed. Benzene 3D Download 3D Benzene was first isolated by Michael Faraday in , from the whale oil used in gaslights; he also determined that it had an empirical formula of CH.
Amygdalin Laetrile 3D Download 3D Amygdalin is a disaccharide consisting of two glucose molecules in which a carbon bearing a cyano CN group and a benzene ring is attached to one of the oxygen atoms on a glucose. Hyacinthin 3D Download 3D Hyacinthin is commonly used in perfumes; it is responsible for the floral scent found in hyacinth oddly enough. Cinnamaldehyde 3D Download 3D Cinnamaldehyde is found in oil of cinnamon, which is found in the bark of the cinnamon tree. Naphthalene 3D Download 3D Naphthalene is a white crystalline solid, derived from coal tar, with a characteristic odor of mothballs — which is not a coincidence, since naphthalene is frequently used in mothballs.
Pyridine 3D Download 3D In the pyridine molecule, one of the CH groups of the benzene ring is replaced with a nitrogen atom. OUT on pyrrole. The energy from the sunlight that is absorbed by chlorophyll in the chloroplasts of green plants is used to drive the synthesis of carbohydrates such as glucose C 6 H 12 O 6 from carbon dioxide and water: This equation summarizes a lot of complex chemistry, which it is beyond the scope of this page to try to summarize.
Download 3D. Buckminsterfullerene 3D Download 3D Buckminsterfullerene , or C 60 , is a soccer-ball shaped molecule consisting of 60 carbon atoms. Larger fullerenes are found to encapsulate lanthanide metal atoms. Interest in the fullerenes has led to the discovery of a related group of carbon structures referred to as nanotubes. As shown in the following illustration, nanotubes may be viewed as rolled up segments of graphite.
The chief structural components are six-membered rings, but changes in tube diameter, branching into side tubes and the capping of tube ends is accomplished by fusion with five and seven-membered rings. Many interesting applications of these unusual structures have been proposed.
A model of a nanotube will be displayed by clicking on the diagram. Many unsaturated cyclic compounds have exceptional properties that we now consider characteristic of "aromatic" systems. The following cases are illustrative:. The first three compounds cyclic polyenes have properties associated with alkenes in general. Each reacts readily with bromine to give addition products, as do most alkenes.
The thermodynamic change on introducing double bonds into the carbon atom ring is also typical of alkenes a destabilization of ca. The remaining four compounds exhibit very different properties, and are considered aromatic. Furan and pyrrole react more rapidly with bromine, but they also give substitution products. This tendency to favor substitution rather than addition suggests that the parent unsaturated ring system has exceptional stability.
Thermodynamic measurements support this conclusion. A planar or near planar cycle of sp 2 hybridized atoms, the p-orbitals of which are oriented parallel to each other. Cyclooctatetraene fails both requirements, although it has a ring of sp 2 hybridized atoms. Angle strain is relieved by adopting a tub-shaped conformation; consequently, the p-orbitals can only overlap as isolated pairs, not over the entire ring. Benzene is the archetypical aromatic compound.
The aromatic heterocycle pyridine is similar to benzene, and is often used as a weak base for scavenging protons. Furan and pyrrole have heterocyclic five-membered rings, in which the heteroatom has at least one pair of non-bonding valence shell electrons.
By hybridizing this heteroatom to a sp 2 state, a p-orbital occupied by a pair of electrons and oriented parallel to the carbon p-orbitals is created. Four illustrative examples of aromatic compounds are shown above. The second and third compounds are heterocycles having aromatic properties. Pyridine has a benzene-like six-membered ring incorporating one nitrogen atom. The last compound is imidazole, a heterocycle having two nitrogen atoms.
The other electron pair colored black behaves similarly to the electron pair in pyridine. Monocyclic compounds made up of alternating conjugated double bonds are called annulenes. Benzene and 1,3,5,7-cyclooctatetraene are examples of annulenes; they are named [6]annulene and [8]annulene respectively, according to a general nomenclature system in which the number of pi-electrons in an annulene is designated by a number in brackets.
Some annulenes are aromatic e. As shown in the following diagram, 1,3,5,7,9-cyclodecapentaene fails to adopt a planar conformation, either in the all cis-configuration or in its 1,5-trans-isomeric form. The transannular hydrogen crowding that destabilizes the latter may be eliminated by replacing the interior hydrogens with a bond or a short bridge colored magenta in the diagram.
Naphthalene and azulene are [10]annulene analogs stabilized by a transannular bond. The bridged [14]annulene compound on the far right, also has aromatic properties. A modified [10]annulene, aromatic by nmr criteria, was prepared recently by chemists at California Institute of Technology. Remarkably, this hydrocarbon is chemically unstable, in contrast to most other aromatic hydrocarbons.
To learn more Click Here. A synthesis of barrelene bicyclo[2. Zimmerman Wisconsin , using a double Hofmann elimination. As shown in the following diagram, the chemical behavior of this triene confirmed it was not aromatic in the accepted sense of this term. Bromine addition took place rapidly with transannular bond formation, in the same fashion as with norbornadiene bicyclo[2. Pyrolysis of barrelene gave the expected cycloreversion products benzene and acetylene.
The heat of hydrogenation of barrelene reflects its thermodynamic stability. Furthermore, the first double bond of barrelene is reduced with the release of An explanation for the lack of aromatic behavior in the case of barrelene may be found by comparing the orbital symmetry of the six component p-orbitals with those of benzene.
Benzene is an annulene in which all six p-orbitals may be oriented with congruent overlapping phases. The cylindrical array of p-orbitals in barrelene cannot be so arranged, as shown in the diagram on the right. There will always be one region a nodal plane in which the transannular overlap is incongruent.
By clicking on this diagram , a Jmol model of barrelene will be displayed in a separate window. This model may be moved about for viewing. The p-orbitals of the double bonds may also be displayed.
As noted above, 1,3,5,7-cyclooctatetraene is non-planar and adopts a tub-shaped conformation. The compound is readily prepared, and undergoes addition reactions typical of alkenes. Catalytic hydrogenation of this tetraene produces cyclooctane. The simple C 8 H 6 hydrocarbon pentalene does not exist as a stable compound, and its hexaphenyl derivative is air sensitive.
Azulene is a stable blue crystalline solid that undergoes a number of typical aromatic substitution reactions. Other examples may be cited. Thus, all attempts to isolate 1,3-cyclobutadiene have yielded its dimer, or products from reactions with other compounds introduced into the reaction system.
Cyclooctatetraene is a fascinating compound. To see more of its chemistry Click Here. Practice Problems. Return to Table of Contents. This page is the property of William Reusch. Comments, questions and errors should be sent to whreusch msu.
These pages are provided to the IOCD to assist in capacity building in chemical education. Recall the definitions of electrophile and nucleophile: Electrophile : An electron deficient atom, ion or molecule that has an affinity for an electron pair, and will bond to a base or nucleophile. Nucleophile : An atom, ion or molecule that has an electron pair that may be donated in bonding to an electrophile or Lewis acid. Many functional groups have weakly electrophilic carbon atoms colored red in the following examples.
These electrophilic functions may react with nucleophiles bases in two distinct ways:. A Frost circle reflects the pattern of orbital energies. You place the ring inside a circle with one of its vertices pointing downwards. Then you draw a horizontal line though the vertices. This represents the orbital energy levels.
You need 2 electrons to fill the first level and 4 electrons to fill each level above the first. Related questions What is the difference between a resonance structure and a resonance hybrid structure? When the aromatic hydrocarbon naphthalene reacts with nitric and sulfuric acids, two compounds What are major resonance structures?
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