Chemistry: Naming Organic Compounds Guided Inquiry -­‐ Teacher’s Notes Nomenclature is the process of naming chemical compounds based on their chemical formula. Formula writing is the reverse process, writing the chemical formula for a compound based on its name. There are different naming rules ionic compounds, molecular compounds and organic compounds. Organic Compounds Organic compounds are any compounds that contain both hydrogen and carbon atoms. They may also contain other elements such as oxygen, sulfur, nitrogen, phosphorus, et cetera. We are only going to learn the naming rules for the simplest groups of organic compounds: alkanes, alkenes and alkynes. Model 1 CH4 CH3 — CH3 CH3 — CH2 — CH3 Compound A (Methane, CH4) Compound B (Ethane, C2H6) Compound C (Propane, C3H8) CH3 — CH2 — CH2 — CH3 CH2 = CH2 CH2 = CH — CH3 Compound D (Butane, C4H10) Compound E (Ethene, C2H4) Compound F (Propene, C3H6) CH3 — CH2 — CH2 — CH2 — CH3 CH ≡ CH CH ≡ C — CH3 Compound G (Pentane, C5H12) Compound H (Ethyne, C2H2) Compound I (Propyne, C3H4) 1. Compare the structural formula (top) and the condensed structural formula (bottom) for each compound. What is different about the two ways of writing the compound? Why is the lower way of writing the compound called the condensed structural formula? The structural formula shows all the bonds, including the bonds between the carbon and
hydrogen atoms, while the condensed structural formula only shows the bonds between the
carbon atoms. The condensed formula is shorter to write.
2. Compare Compounds A, B, C, D and G. List two things that are different about these compounds? The number of carbon atoms and the number of hydrogen atoms are different.
3. What do Compounds B, E and H have in common? They all have two carbon atoms.
4. What do Compounds C, F, and I have in common? They all have three carbon atoms.
5. What does the first part of the name tell us about the compound? It tells us the number of carbon atoms in the compound.
6. Compare Compound B, E and H. List two things that are different about these compounds? The number of hydrogen atoms and the type of bonds are different. E has a double bond, H
has a triple bond, while B has all single bonds.
7. Compare Compounds C, F and I. List two things that are different about these compounds? The number of hydrogen atoms and the type of bonds are different. F has a double bond, I
has a triple bond, while C has all single bonds. 8. What does the second part of the name tell us about the compound? It tells us if the compound has all single bonds, a double bond or a triple bond.
9. Which of the 9 compounds in Model 1 are alkanes? What makes them alkanes? Compounds A, B, C, D and G are alkanes because they have all single bonds.
10. Which of the 9 compounds in Model 1 are alkenes? What makes them alkenes? Compounds E and F are alkenes because they have a double bond.
11. Which of the 9 compounds in Model 1 are alkynes? What makes them alkynes? Compounds H and I are alkynes because they have a triple bond.
Model 2 Name Formula Name Formula Name Formula Methane CH4 Ethane C2H6 Ethene C2H4 Ethyne C2H2 Propane C3H8 Propene C3H6 Propyne C3H4 Butane C4H10 Butene C4H8 Butyne C4H6 Pentane C5H12 Pentene C5H10 Pentyne C5H8 Hexane C6H14 Hexene C6H12 Hexyne C6H10 Heptane C7H16 Heptene C7H14 Heptyne C7H12 Octane C8H18 Octene C8H16 Octyne C8H14 Nonane C9H20 Nonene C9H18 Nonyne C9H16 Decane C10H22 Decene C10H20 Decyne C10H18 12. Write the prefix for a compound containing the following number of carbon atoms: a. two carbons -­‐ eth c. eight carbons -­‐ oct b. five carbons -­‐ pent d. nine carbons -­‐ non 13. Write the suffix for each type of compound (refer to Model 1 and Model 2). a. a compound with all single bonds – ane b. a compound with one double bond – ene c. a compound with one triple bond -­‐ yne 14. Why aren’t there other compounds listed in the same row as methane in Model 2? To have a double bond or triple bond you need to have more than one carbon atom and the
first row shows compounds with one carbon.
It may be helpful to refer to both Model 1 and Model 2 to answer #15 through #17. 15. Compared to the number of carbon atoms, how many hydrogen atoms are there in alkane compounds? The # of hydrogen atoms = 2n + 2, where n is the # of carbon atoms.
16. Compared to the number of carbon atoms, how many hydrogen atoms are there in alkene compounds? The # of hydrogen atoms = 2n, where n is the # of carbon atoms.
17. Compared to the number of carbon atoms, how many hydrogen atoms are there in alkyne compounds? The # of hydrogen atoms = 2n - 2, where n is the # of carbon atoms. Model 3 Name Condensed Structural Formula Name Condensed Structural Formula Ethyne CH ≡ CH Hex-­‐1-­‐yne CH ≡ C — CH2 — CH2 — CH2 — CH3 Propene CH2 = CH — CH3 Hex-­‐2-­‐yne CH3 — C ≡ C — CH2 — CH2 — CH3 But-­‐1-­‐ene CH2 = CH — CH2 — CH3 Hex-­‐3-­‐yne CH3 — CH2 — C ≡ C — CH2 — CH3 But-­‐2-­‐ene CH3 — CH = CH — CH3 Hex-­‐2-­‐yne CH3 — CH2 — CH2 — C ≡ C — CH3 But-­‐1-­‐ene CH3 — CH2 — CH = CH2 Hex-­‐1-­‐yne CH3 — CH2 — CH2 — CH2 — C ≡ CH 18. What is the purpose of the numbers in the names of the compounds in Model 3? The number shows where the double or triple bond is located in the carbon backbone. The
number represents the carbon (counting from the left) and the bond comes after that
carbon.
19. Why don’t you need a number for the first two compounds, ethyne and propene? There is only one place for the double or triple bond and that’s after the first carbon.
20. Why is the compound at the bottom of the first column named but-­‐1-­‐ene instead of but-­‐3-­‐ene? If you rotate the molecule 180 degrees the carbon on the right end becomes the carbon on
the left end. There is no difference between the carbon atoms on each end of the molecule.
So in both instances the double bond comes after the first carbon atom.
21. In the second column, why are the last two compounds called hex-­‐2-­‐yne and hex-­‐1-­‐ene instead of hex-­‐4-­‐ene and hex-­‐5-­‐ene? For the second to last compound, there is no difference between the second carbon atom
from the left and the second carbon atom from the right. In both instances the triple bond
comes after the second carbon atom. For the last compound, there is no difference
between the carbon atom on the right end and the carbon atom on the left end. In both
instances the double bond comes after the first carbon atom.
22. Complete the table below: Name Formula Condensed Structural Formula C7H14
CH3 – CH = CH – CH2 – CH2 – CH2 – CH3 ethane
C2H6 CH3 – CH3
non-4-yne
C9H16 CH3 – CH2 – CH2 – C ≡ C – CH2 – CH2 – CH2 – CH3 octane C8H18 CH3 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH3
pent-­‐2-­‐yne C5H8 CH – CH = CH – CH2 – CH3 pentane
C5H12 CH3 – CH2 – CH2 – CH2 – CH3 ethyne C2H2 HC ≡ CH
propyne C3H4 CH3 – C ≡ CH
hept-­‐1-­‐yne C7H12 CH2 = CH – CH – CH2 – CH2 – CH2 – CH3
non-3-yne C9H16 CH3 – CH2 – C ≡ C – CH2 – CH2 – CH2 – CH2 – CH3 hex-3-ene C6H10 CH3 – CH2 – CH = CH – CH2 – CH3 decane C10H22 CH3 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH3
hept-2-ene