How many isomers does pentantetraol have?

Answer 1

Pentanoic acid has 4 carbon atoms with 7 H's bonded to them and 1 carbon atom with a carboxyl ion bonded to it.

In the drawings below, I have left off all the single bonded H's to simplify the drawing.

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Go to this web site to see a carboxylic group or do a Google search for carboxylic group.

http://www.ch.ic.ac.uk/vchemlib/mol/glossary/carboxyl.gif

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A carboxyl ion is a carbon atom with one oxygen atom double bonded to it, and an O-H single bonded to it as shown below. It has a -1 charge as shown by the - mark to the left of the C. The - ark actually represents one unpaired electron desiring to find another atom with one unpaired electron.

…..H

…..!

….O

….!

...-C=O

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Isotope #1

Draw a row of 4 carbon atoms.

Attach a carboxyl ion to the #1 C atom of the 4 you drew.

Now the structure has 5 C atoms in a row.

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…...H

…...!

O=C-C-C-C-C

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Attaching a carboxyl ion to #4 C is the same as attaching a carboxyl ion to the #1 C atom. (depending on what side of the table you are sitting on, right becomes left)

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………….H

……….…!

C-C-C-C=O-H

Isotope #2

Attaching a carboxyl ion to the #2 C atom is the same as attaching a carboxyl ion to the #3 C atom.

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…....H

....….!

....…O

….....!

C-C-C-C

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…….H

…….!

……O

……!

C-C-C-C

Isotope #3

Draw a row of 3 carbon atoms, with 1carbon atom bonded below #2 C atom. Attach the carboxyl ion above the #2 C atom. I see 3 carbon atoms in a horizontal line or 3 carbon atoms in a vertical line. There are 4 carbon atoms attached to a central carbon atom. No matter where I attach the double bond O, single bond H, it is attached to one of these 4 carbon atoms.

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…H

….!

….C=O-H

….!

C-C-C

…!

...C

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There only 3 isotopes

Draw a line of 5 C's

…..2..3..4

-C-C-C-C-C-

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You might wonder why you can not attach a double bond O, single bond H to Carbon atoms #2, #3,or #4. Looking at the carboxyl ion below, how many bonds does the carbon have around it? I see 3 bonds. (double bond O (2), single bond H (1)) A carbon can only make 4 bonds. If you try to attach a carboxyl ion to Carbon atoms #2, #3, or #4, you still need 2 bonds to attach to the Carbon atoms on the left and right side of that carbon.

…..H

…..!

….O

….!

...-C=O

If you can get a molecular model you can build these isotopes and, determine how many different isotopes you can make.

Answer 2

Pentantetraol, with the chemical formula C5H12O4, has a total of 30 isomers.