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A valid name survives the round trip — draw it, name the drawing, get the same name back; names also give formulas, which say whether two compounds are the same, isomers, or different.
Paper packet. Every task here also exists on screen, where it is checked automatically; answers written on paper are not assessed by Nydus. When you are back at a device, enter your answers there.
You will correct faulty names by the round trip, count atoms from a name, spot invalid names, and decide whether two named compounds are the same, isomers, or different.
You can name a molecule from its structure. This lesson runs the process backwards, and then both ways round, as a check.
The round trip is drawing a structure from a name, then naming the drawing again: a valid name returns unchanged. Connectivity is which atoms are joined to which. Structural isomers share a molecular formula and differ in connectivity.
A name is a set of instructions. 2-ethylbutane says: four carbons in a row, an ethyl group on carbon 2. Draw that — CH3CH(CH2CH3)CH2CH3 — and name it from scratch. The longest chain runs through the ethyl group: five carbons, with a methyl on carbon 3. The drawing is 3-methylpentane, so '2-ethylbutane' failed the round trip.
The common failures:
Another way: steps
To check a name:
A name gives the formula too. 3-ethyl-2-methylhexane has six parent carbons plus two plus one, nine in all, and as an alkane C9H20. That makes names a quick way to compare compounds: if two names give the same structure, they are the same compound; if they give the same formula and a different structure, the compounds are isomers with different properties; if the formulas differ, they are simply different compounds. Butan-1-ol boils at 118 °C and its isomer 2-methylpropan-2-ol at 82 °C: same formula, different substances.
Two names that sound similar must describe the same connectivity. Draw them and see.
The same formula means the same compound. Isomers share formulas.
A name is correct if it can be drawn. It must also be the name that drawing would get.
Branch carbons don't count in the formula. Every carbon counts.
Draw a four-carbon chain with CH3 on carbon 1: CH3CH2CH2CH2CH3.
Exactly what it says.
The longest chain is now five carbons with no branch at all.
Find the true chain.
The drawing is pentane, so '1-methylbutane' fails the round trip.
Rename and compare.
Draw it: four carbons, a methyl on carbon 3.
CH3CH2CH(CH3)CH3.
Number from the other end. Where is the methyl now?
On carbon 2: it is 2-methylbutane.
A student names a compound 4-methylhexane. Draw the structure that name describes, then give its correct name.
The correct name is n.
How many carbon atoms are in 3-ethyl-2-methylpentane?
Answer:
Match each pair of names to how the compounds they describe are related.
| the same compound | structural isomers: same formula, different connections | different compounds with different formulas | |
|---|---|---|---|
| pentane and 2,2-dimethylpropane | |||
| butan-1-ol and butan-2-ol | |||
| propane and propene | |||
| 2-methylbutane and CH3CH(CH3)CH2CH3 |
A worksheet lists four names. Mark every name that cannot be correct as written.
This task has no paper form; do it on a device.
Two bottles in a store are labelled butan-1-ol and 2-methylpropan-2-ol. A technician says they must hold the same substance because both are C4H10O. Is that right?
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
How many hydrogen atoms does one molecule of 3-ethylpentane contain?
One molecule contains a hydrogen atoms.
You can use a name to test a structure. Tell someone why 2-ethylbutane is not a correct name. Next unit: what happens when a molecule rotates about its single bonds.
8. Your turn: check '3-methylbutane', step 3