Dr. Glaser's "Chemistry is in the News"
To Accompany Bruice, Organic Chemistry, 3/e.
Chapter 5. Reactions of Alkynes. Introduction to Multistep Synthesis.

Editorial Comments

San Francisco. The City. This jewel among American cities. You have to love San Francisco for its beauty and its cultural richness and all the Arts & Entertainment it offers. Concerts, ballet, theater and plenty of museums! Something for everybody and something else for every day!

The only fault of the city is that it sits on one, a continental fault that is, and earthquakes strike all the time. Mostly little ones that don't get you excited beyond mild amusement. But remember the "Little Big One" of 1989! That earthquake measured 7.2 on the Richter scale. Not so little.

Plenty of damage was done and some repairs are only now coming to completion. The restoration of the San Francisco War Memorial Opera House is the subject of the present news story. As you can read in the Herald Tribune, the seismic retrofit was only one item of the greater restoration that also included renovation of stage equipment and facilities and the restoration of the Beaux Arts interior. The renovation merges tradition and the classical arts with the benefits of modern audio technology. Take a look at the images from the renovation and see how "computer renditions depicting speaker throw patterns from the CQ-1 and CQ-2 speakers" were used to assure best sound.

"What does all this have to do with chemistry?" you may ask. Very much indeed. Next time you travel to the City and attend a show at the San Francisco War Memorial Opera House sit in the mezzanine. A fire set by a worker's acetylene torch in the mezzanine-box tier made necessary a more ambitious renovation than had been planned in that area. And you are getting to enjoy all the benefits of that more ambitious renovation. Enjoy the ambience, enjoy the show, and ... psst ... be quiet, please, the show is about to start ...

Questions

Question 1: Explain the bonding of acetylene using the theory of hybridiation.

Answer 1: The C-atoms on acetylene are sp hybridized. The C-C sigma bond is formed by overlap between two C sp-hybrid orbitals. Each C-atom still has two p-atomic orbitals and these are used to form two C-C pi-bonds. The C-H bonds are sigma bonds formed between a C sp-hybrid orbital and am s orbital of hydrogen.

Question 2: Explain the principle of an acetylene torch. Provide a stoichiometric equation for the complete combustion of acetylene.

Answer 2: The acetylene torch employs the controlled burning of an acetylene stream in an oxygen stream. The complete combustion of acetylene is described by the equation C₂H₂ + 2.5 O₂ --> 2 CO₂ + H₂O. The temperature of the flame produced by the acetylene torch can be as high as 3000 degree Celsius.

Question 3: If you burn acetylene in the regular atmosphere and without an additional oxygen stream, then the burning is quite different. The flame is much less hot and there is a lot of thick black smoke produced. What kind of combustion might be happening?

Answer 3: Incomplete combustion. Instead of CO₂, the carbon-containing products of decombustion are CO (a toxic colorless gas) and C itself (in the form of soot).

Question 4: In industry, acetylene is a central commodity. Acetylene is the starting material for many chemicals that are produced in large scale. Acetaldehyde, H₃C-CH=O, is made from acetylene. Do you know what reaction converts acetylene into acetaldehyde?

Answer 4: Acid-catalyzed hydration. You make the "enol" which then tautomerizes to the "keto" form.

Chemistry & Comics.
Question 5: Looking for an interesting story that might connect "acetylene" to society, not an easy task, I came across the website Acetylene Comics. I am not quite clear how that name came about. But the website reminded me of other websites such as The Periodic Table of the Comic Books and Humor in Chemistry. Some think that the comic format or the humorous context makes chemistry attractive to an audience that might otherwise not be intersted in chemistry at all. Do you agree or disagree?