Aromatic Hydrocarbons The benzene compounds. So far, everything we’ve looked at was ALIPHATIC...
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Transcript of Aromatic Hydrocarbons The benzene compounds. So far, everything we’ve looked at was ALIPHATIC...
• So far, everything we’ve looked at was ALIPHATIC
• About 100 years ago, chemists became aware of a group of nice-smelling compounds-the AROMATICS
• Today we know that many aromatics stink
• 1825-the British chemist Faraday discovered a compd in whale oil
• Its formula was C6H6
• They knew that it wasn’t very reactive
• Alkanes unreactive
• Alkenes somewhat reactive
• Alkynes very reactive
• BUT, Benzene wasn’t reactive
• Also, benzene couldn’t be drawn as a saturated molecule
• How do you draw benzene with no double or triple bonds?
• 1865-German chemist name Kekule’ went home one day, sat down by his fireplace, and went to sleep
• He had a dream in which he was out walking in the country
• He saw a SNAKE!!
• He decided to outwalk it, but the SNAKE chased him!
• Up ahead Kekule’ saw a cliff
• He ran up to the edge and jumped off!!
• The SNAKE got to the edge, and looked down at him with an evil look
• He put his tail in his mouth and rolled down the hill!!
• Kekule’ woke up and had the answer to his C6H6 problem
• See structures on the board
• Skeptics asked, “how do you know which one it is?”
• X-ray diffraction analysis-allows us to measure bond length between carbons.
• The C-C bond is normally longer than the C=C
• BUT, in benzene, it was found that the C-C’s were shorter than normal and the C=C’s were longer
• The real structure of benzene is a hybrid of the 2-see board
• Resonance: the representation of a real structure by the average of 2 or more fictitious Lewis structures.
• The true structure-a composite of the contributing structures-is called the resonance hybrid.
• Resonance indicates stability.
• Why is resonance important?
• It helps chemists visualize the actual molecule as a hybrid.
• Magnetic Resonance Imaging
• -article of bad MRI
• Show a real one vs. x-ray
• Naming Aromatics is fun.
• Monosubstituted benzenes-NO2 -Br -Cl
-CH3 -NH2 -OH -COOH
• Be sure to know – Toluene– Phenol– Aniline– Benzoic Acid
Disubstituted Benzenes
• If a common name (toluene, aniline, phenol, benzoic acid) is present, use is at the parent name.
• These have special rules– Ortho or o (1,2)– Meta or m (1,3)– Para or p (1,4)
– OMP can only be used when 2 groups are on the ring!!– http://www.youtube.com/watch?
v=HPGE_GJkLJA&feature=related cheesy video
Polysubstituted Benzenes
• When a common name (toluene, aniline, benzoic acid, phenol) is present, use it as a parent name
The Phenyl Group
• Benzene can also be named as a side group.
• It’s not called “benzyl” as you would expect!
• Instead we call it “phenyl”– Phenyl is not the same as phenol
• Exs:– Phenyl chloride
– Diphenyl methane
– m-phenyl phenol
– Dichlorodiphenyltrichloroethane-moral story• DDT info 3 min video• http://videos.howstuffworks.com/hsw/15861-aggrav
ation-of-accumulation-ddt-and-bald-eagles-video.htm
Practice/review drawing these!
• 1. o-dichlorobenzene• 2. m-bromophenol• 3. p-xylene• 4. 1,2-difluoro-3-iodobenzene• 5. 2,3-dinitroaniline• 6. o-phenyltoluene• 7. m-dibenzylbenzene• 8. phenyl bromide• 9. o-phenyl phenol
Fused Aromatics
• Some compounds have 2 or more benzene rings fused together
• Exs:– Naphthalene
• In mothballs, a solid at room temperature
Cig smoke, car exhaust, and burned food all contain fused aromatics
So does chimney soot-testicular cancerMary Poppins videohttp://www.youtube.com/watch?v=yu23HHmOG48Same guyshttp://www.youtube.com/watch?v=xRYU4cqUAUs
More on DDT
• It’s colorless, odorless, tasteless• Banned in US but still used in some
underdeveloped countries• Has saved lives by killing disease-carrying
insects (lice, ticks, mosquitoes)• Worst thing about it is stability• Biological magnification• How DDT kills birds
Misc Interesting Stuff
• PABA (p-aminobenzoic acid) in some sunscreens• Various forms of sunscreen have been around for
thousands of years. Ancient Egyptians used jasmine as a sunscreen, and ancient Greeks rubbed olive oil on their skin for protection.
• chemical sunscreens (avobenzone,benzophenone) absorb the sun's harmful UV rays while physical sunscreens, or sunblocks (zinc oxide, titanium dioxide), reflect them.
• Broad spectrum sunscreens contain both types (above)• SPF-skin protection factor-doesn’t account for wind, angle
of sun, elevation, or reflection• Min recommended SPF is 15
Natural sunscreen?Melanin-a dark-colored skin pigment that offers natural protection
from the sunIt’s why we’re all colored people! Well, most of us Albinos have a birth defect they don’t have melanin
http://videos.howstuffworks.com/discovery/30903-why-tell-me-why-why-skin-color-varies-video.htm
Makes up hair color, skin color, and eye colorAlso makes up freckles
Bad stuff
• Tanning beds give off same kind of radiation as sun
Miss Maryland and melanoma-3 minhttp://videos.howstuffworks.com/multivu/1844-melanoma-video.htmShould you get a tan? 14 minhttp://videos.howstuffworks.com/planet-green/37339-g-word-organic-spray-tan-video.htmSunburns are bad 1 minhttp://videos.howstuffworks.com/howstuffworks/131-how-sunburns-work-video.htm
Good stuff
• Our body needs some aromatics-we get them from our diet ex: vitamins
• You need sunlight-1.5 min videos-see which one is better
• http://videos.howstuffworks.com/sciencentral/4149-how-not-getting-enough-sun-can-be-harmful-video.htm
• http://videos.howstuffworks.com/discovery-health/32522-cleveland-clinic-2008-vitamin-d-video.htm