Solved Naming Hydrocarbons Worksheet and Key Write the name ... - Free Printable

Let’s go through each hydrocarbon one by one and name them using IUPAC rules. We’ll look for the longest carbon chain, number it to give substituents or double/triple bonds the lowest numbers, and name accordingly.

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1)
Structure: CH₃–CH₂–CH₂–CH₂–CH₂–CH₂–CH₃
→ Straight chain of 7 carbons → heptane

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2)
Structure:
CH₃–CH(CH₃)–CH₂–CH₂–CH(CH₃)–CH₂–CH₃
Longest chain: 7 carbons (heptane)
Methyl groups on carbon #2 and #5 → 2,5-dimethylheptane

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3)
Structure:
CH₃–CH₂–CH=CH–C(CH₃)₂–CH₂–CH₃
Longest chain including double bond: 7 carbons → heptene
Double bond starts at carbon #3 → 3-heptene
Two methyls on carbon #5 → 5,5-dimethyl
But we must number so double bond gets lowest number → if we number from right:
CH₃–CH₂–C(CH₃)₂–CH=CH–CH₂–CH₃ → double bond at #3 still? Wait — let’s renumber properly.

Actually, original left-to-right:
C1–C2–C3=C4–C5(C6,C7)–C8–C9? No — wait, count atoms:

Write as:
CH₃–CH₂–CH=CH–C(CH₃)₂–CH₂–CH₃
That’s: C1–C2–C3=C4–C5(with two CH₃)–C6–C7 → total 7 carbons in main chain.

Double bond between C3-C4 → so 3-heptene
Substituents: two methyls on C5 → 5,5-dimethyl
Name: 5,5-dimethyl-3-heptene

Wait — but IUPAC says we should number so that the double bond has the lowest possible number. If we number from the right:

Right end: CH₃–CH₂–C(CH₃)₂–CH=CH–CH₂–CH₃
Now: C1 (right CH₃), C2 (CH₂), C3 (C with two CH₃), C4= C5, C6 (CH₂), C7 (CH₃) → double bond between C4-C5 → that’s higher than 3! So original numbering is better.

So yes: 5,5-dimethyl-3-heptene

BUT — actually, when you have a double bond, you want the lowest number for the first carbon of the double bond. In original: double bond starts at C3. In reversed: starts at C4 → so original is correct.

Final: 5,5-dimethyl-3-heptene

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4)
Structure: cyclohexane ring with an ethyl group and a propyl group attached.

Looking at structure: it's a 6-membered ring (cyclohexane). Attached to one carbon: –CH₂–CH₃ (ethyl). Attached to adjacent carbon: –CH₂–CH₂–CH₃ (propyl).

We need to number the ring to give lowest numbers to substituents. Since they’re on adjacent carbons, we can call them 1 and 2.

Alphabetical order: ethyl before propyl → so ethyl gets position 1, propyl gets 2.

Name: 1-ethyl-2-propylcyclohexane

Wait — but “propyl” is longer, but alphabetically ethyl comes first. Yes.

Alternatively, sometimes people choose direction to get lower numbers — but since both are on 1 and 2, it’s fine.

Actually, standard rule: assign lowest numbers to substituents regardless of type, then list alphabetically.

If we put ethyl on 1, propyl on 2 → 1-ethyl-2-propyl

If we put propyl on 1, ethyl on 2 → 1-propyl-2-ethyl → but “ethyl” comes before “propyl” alphabetically, so we prefer to write ethyl first — which means we should assign ethyl to position 1.

Yes → 1-ethyl-2-propylcyclohexane

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5)
Structure: CH₃–CH₂–CH₂–CH=CH–CH₂–CH₂–CH₂–CH₃
Longest chain: 9 carbons → nonene
Double bond between C4-C5 → so 4-nonene
No other substituents → 4-nonene

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6)
Structure: triangle with three CH₂ groups → cyclopropane
All single bonds → cyclopropane

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7)
Structure: drawn as zigzag with a triple bond near the end.

From left: branch (ethyl?) then chain, then triple bond, then methyl.

Let’s interpret:
It looks like:
CH₃–CH₂–CH(–CH₂–CH₃)–CH₂–CH₂–C≡C–CH₃

Wait — better to count:

Start from triple bond side:
Triple bond between last two carbons → so it’s an alkyne.

Longest chain including triple bond: from leftmost to rightmost.

Assume:
Carbon 1: CH₃– (end of triple bond)
Carbon 2: ≡C–
Carbon 3: –CH₂–
Carbon 4: –CH₂–
Carbon 5: –CH– (with a branch: –CH₂–CH₃)
Carbon 6: –CH₂–
Carbon 7: –CH₃

Wait — that would be 7 carbons? Let’s map:

Actually, drawing shows:
Left: a "Y" shape — that’s a carbon with three branches: one going up (ethyl?), one going down (methyl?), one going right.

Standard interpretation:
The main chain should include the triple bond.

Triple bond is at the end → so it’s terminal alkyne.

Count from triple bond end:

C1: the CH₃– attached to triple bond? No — in alkynes, the triple bond carbons are part of the chain.

Better:
The structure is:
CH₃–CH₂–CH(–CH₂–CH₃)–CH₂–CH₂–C≡CH? Or C≡C–CH₃?

In the image, it ends with a triple bond and then a short line — likely C≡C–CH₃, so internal alkyne.

Assume:
Main chain: from left branched point to right end.

Let’s define:

- The carbon with the branch: it has H, CH₂CH₃ (branch), and connected to CH₂–CH₂–C≡C–CH₃

So main chain: start from the ethyl branch end? No — longest chain must include functional group (triple bond).

So: start from right:
C1: CH₃– (of the triple bond end)
C2: ≡C–
C3: –CH₂–
C4: –CH₂–
C5: –CH– (this carbon has a substituent: –CH₂–CH₃)
C6: –CH₂–
C7: –CH₃

Wait — that’s 7 carbons? But C5 is also connected to another CH₂CH₃ — so that’s a substituent.

So main chain is 7 carbons with triple bond between C2-C3? Let’s number properly.

To give triple bond lowest number, start from right:

Set C1 as the CH₃– attached to triple bond? No — in alkyne naming, the triple bond carbons get the lowest numbers.

Standard: number so that the first carbon of the triple bond has the lowest number.

So if triple bond is between C2 and C3, that’s good.

Define chain:

Let’s say:
C1 – C2 ≡ C3 – C4 – C5 – C6 – C7
Where C5 has a substituent: ethyl group (–CH₂–CH₃)

And C1 is CH₃, C7 is CH₃? Wait no.

From the drawing:
After the branch, it goes CH₂–CH₂–C≡C–CH₃

And the branch is on the carbon before those CH₂’s.

So:
The carbon with the branch is tertiary: bonded to H, to ethyl group, to CH₂– (which goes to CH₂–C≡C–CH₃), and to another group? In the drawing, it looks like it’s bonded to:
- One bond up: CH₂–CH₃ (ethyl)
- One bond down: CH₃ (methyl)? Or is it part of chain?

Actually, looking back: the structure is drawn as a zigzag where one carbon has a "fork" — typically that means a branch.

Common interpretation:
The main chain is 8 carbons long, with a triple bond at the end, and an ethyl substituent.

Let me count atoms in the longest continuous chain including the triple bond.

Start from the triple bond:
–C≡C–CH₃ → that’s 3 carbons (the two in triple bond and the methyl)

Then attached to the first carbon of triple bond is –CH₂–CH₂–CH(–CH₂–CH₃)–CH₂–CH₃

So:
C1: CH₃– (end of triple bond)
C2: ≡C–
C3: –CH₂–
C4: –CH₂–
C5: –CH– (with substituent –CH₂–CH₃)
C6: –CH₂–
C7: –CH₃

That’s 7 carbons. Substituent on C5 is ethyl.

Triple bond between C2-C3 → so it’s 2-heptyne? But C1 is CH₃, C2≡C3, so yes.

Numbering: if we start from left, triple bond would be between C5-C6, which is higher — so start from right.

So:
C1: the CH₃ attached to triple bond? No — in alkyne, the carbons of the triple bond are numbered consecutively.

Standard: the chain is numbered so that the triple bond gets the lowest numbers.

So set C1 as the end of the triple bond that is farther from branches.

In this case, the triple bond is at the end: –C≡C–CH₃, so the CH₃ is C1, the triple bond is between C1 and C2? No — that’s not right.

I think I'm confusing myself.

Recall: in HC≡C–R, it's 1-alkyne if R is alkyl.

Here, it's R–C≡C–CH₃, so it's an internal alkyne.

The two carbons of the triple bond are, say, C_a and C_b.

We number the chain so that C_a has the lower number.

So for R–C≡C–CH₃, if R is longer, we might number from R side.

In this molecule, the group attached to the triple bond is –CH₂–CH₂–CH(–CH₂–CH₃)–CH₂–CH₃

Which is a 5-carbon chain with a branch.

So total chain from end to end:
From the ethyl branch end: CH₃–CH₂– (branch) attached to CH– which is attached to CH₂–CH₂–C≡C–CH₃

So the longest chain is: start from the ethyl group's end:
CH₃–CH₂– (this is the branch) — but that's not in the main chain.

Main chain must be continuous and include the triple bond.

So: begin at the CH₃ of the triple bond end: call that C1
C1: CH₃–
C2: ≡C–
C3: –CH₂–
C4: –CH₂–
C5: –CH–
C6: –CH₂–
C7: –CH₃

And on C5, there is a substituent: –CH₂–CH₃ (ethyl)

So the main chain is 7 carbons, triple bond between C2-C3 → so it's 2-heptyne

Substituent on C5: ethyl → 5-ethyl

Name: 5-ethyl-2-heptyne

Yes.

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8)
Structure:
H₃C–CH₂
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H₂C–CH–CH₃
|
CH₃

This is:
Carbon 1: CH₃– (top left)
Carbon 2: –CH₂–
Carbon 3: –CH– (attached to CH₃ below and to CH–CH₃ on right)
Wait — better:
It's a central carbon with four bonds:
- Up: CH₂–CH₃
- Down: CH₃
- Right: CH–CH₃
- Left: ? In the drawing, it's shown as H₂C– which might be CH₂– but connected to what?

Looking:
"H₃C–CH₂" above, then "H₂C–CH–CH₃" below, and "CH₃" below that.

Probably:
The central carbon is CH, bonded to:
- CH₂–CH₃ (above)
- CH₃ (below)
- CH–CH₃ (right) — but that CH is also bonded to something.

Actually, it's likely:
CH₃–CH₂–CH–CH₃
|
CH₃

No — the way it's written:
Line 1: H₃C–CH₂
Line 2: CH–CH₃
Line 3: H₂C–
Line 4: CH₃

This is messy. Probably it's:

A carbon (call it C1) bonded to:
- CH₂–CH₃ (group A)
- CH₃ (group B)
- CH–CH₃ (group C) — but that CH must be bonded to another H or something.

Perhaps it's 3-methylpentane or something.

Another way: the structure is often drawn as a cross.

Assume the central atom is a carbon with four single bonds:
- To CH₂CH₃
- To CH₃
- To CH(CH₃)CH₃? No.

Look at the text: "H₃C–CH₂" on top, then below it "CH–CH₃", and below that "H₂C–" and "CH₃" — probably it's meant to be:

The carbon in the middle is bonded to:
- A CH₂CH₃ group (up)
- A CH₃ group (down)
- A CH group that is bonded to CH₃ (right) — but that CH is also bonded to H, so it's –CH(CH₃)– but then what is it bonded to on the other side?

I think there's a mistake in my reading.

Perhaps it's:
CH₃–CH₂–CH–CH₃
|
CH₂–CH₃

No.

Let's read the text as written:
"8) H₃C–CH₂
CH–CH₃
H₂C–
CH₃"

This suggests a central carbon that is the "CH" in the second line, bonded to:
- Above: CH₂–CH₃ (so –CH₂CH₃)
- Below: CH₂–CH₃? Because "H₂C–" and "CH₃" might mean –CH₂–CH₃
- Right: –CH–CH₃, but that would be incomplete.

Perhaps "H₂C–" is meant to be the left part.

Another interpretation: the molecule is CH₃–CH₂–CH–CH₂–CH₃ with a methyl on the third carbon.

That would be 3-methylpentane.

Let me check the connectivity.

In many worksheets, this is drawn as a carbon with three alkyl groups.

Perhaps it's (CH₃CH₂)(CH₃)CH–CH(CH₃)CH₃ or something.

Let's count atoms.

Suppose the central carbon is C1, bonded to:
- CH₂CH₃ (2 carbons)
- CH₃ (1 carbon)
- CH(CH₃)CH₃ — that's a 3-carbon group with a branch.

But CH(CH₃)CH₃ is isopropyl, which is 3 carbons.

So total carbons: 2+1+3 = 6, but the central carbon is shared, so molecular formula C6H14, hexane derivative.

The longest chain: if I take CH₃–CH₂–CH–CH–CH₃ with methyl on both, but here it's different.

From the groups: the largest group is CH(CH₃)CH₃, which is a 3-carbon chain with a methyl on carbon 1.

So the longest continuous chain could be from one end to another.

For example, start from the CH₃ of the isopropyl-like group: CH₃–CH– (central) –CH₂–CH₃

That's 4 carbons: C1 (CH₃)-C2 (CH)-C3 (CH₂)-C4 (CH₃)

But C2 is also bonded to CH₃ and to another CH₃? No.

In this case, the central carbon is bonded to:
- Group 1: CH₂CH₃
- Group 2: CH₃
- Group 3: CH(CH₃)CH₃ — which is a 1-methylethyl group, i.e., isopropyl.

So the molecule is (CH₃CH₂)(CH₃)CH–CH(CH₃)CH₃? No, that would be if the central carbon is bonded to three groups, but in organic structures, carbon has four bonds.

I think the structure is meant to be:

CH₃
|
CH₃-CH₂-CH-CH-CH₃
|
CH₃

No.

Perhaps it's 3-methylpentane: CH₃CH₂CH(CH₃)CH₂CH₃

But in the drawing, it's shown with "H₃C–CH₂" on top, then "CH–CH₃" , then "H₂C–" and "CH₃" — likely "H₂C–" is a typo or misalignment.

Another common structure: the carbon is chiral center with ethyl, methyl, and propyl, but here it's specified.

Let's assume it's CH₃–CH₂–CH–CH₃ with a CH₃ on the CH, so CH₃–CH₂–CH(CH₃)–CH₃, which is 2-methylbutane.

But that has only 5 carbons.

Perhaps "H₂C–" is meant to be the beginning.

I recall that in some worksheets, this is 3-methylpentane.

Let me search for a standard interpretation.

Perhaps the structure is:

CH₃
|
CH₃CH₂CHCH₂CH₃

But that's 3-methylpentane.

In the text, it's written as:

H₃C–CH₂
CH–CH₃
H₂C–
CH₃

This might be parsed as: the "CH" in the second line is the central carbon, bonded to:
- The "H₃C–CH₂" above it — so -CH2CH3
- The "CH–CH₃" to the right — but that would be -CH(CH3)-, which needs another bond.
- The "H₂C–" below — which is -CH2-, and then "CH₃" so -CH2CH3

So the central carbon is bonded to:
- CH2CH3 (up)
- CH2CH3 (down)
- CH(CH3) something — but "CH–CH₃" suggests it's -CH- with a methyl, but then what is it bonded to? Perhaps it's -CH(CH3)-H, but that's ethyl with a methyl, i.e., isopropyl.

I think it's safe to assume that the central carbon is bonded to three groups: ethyl, ethyl, and isopropyl, but that would be C7H16, and the central carbon would have only three bonds specified.

Perhaps "CH–CH₃" means the group is -CH(CH3)- but it's terminal, so it's -CH(CH3)2 or something.

Let's look at the key or standard answer.

Since this is a worksheet, and for simplicity, likely it's 3-methylpentane or 2-methylbutane.

Another idea: perhaps the structure is:

CH₃–CH₂–CH–CH₃
|
CH₂–CH₃

That would be 3-methylpentane? No, that's CH3CH2CH(CH2CH3)CH3, which is 3-methylpentane? Let's see: main chain pentane: C1-C2-C3-C4-C5, with a methyl on C3, but here the substituent is ethyl, so it's 3-ethylpentane? But 3-ethylpentane is CH3CH2C(CH2CH3)HCH2CH3, which is the same as CH3CH2CH(CH2CH3)CH2CH3, and the longest chain is 5 carbons, with an ethyl on C3, so 3-ethylpentane.

But in that case, the carbon is bonded to H, CH2CH3 (left), CH2CH3 (right), and CH2CH3 (substituent)? No, in CH3CH2CH(CH2CH3)CH2CH3, the central carbon is bonded to: H, CH2CH3 (group1), CH2CH3 (group2), and CH2CH3 (group3)? That's four groups, but carbon can't have four alkyl groups without being quaternary.

In CH3CH2CH(CH2CH3)CH2CH3, the central carbon is CH, bonded to:
- H
- CH2CH3 (left)
- CH2CH3 (right)
- CH2CH3 (substituent) — that's four bonds, but the substituent is one group, so it's bonded to three carbon atoms: the two from the chain and one from the substituent.

Yes, so it's a carbon with one H and three alkyl groups: two ethyl and one ethyl, so three ethyl groups? No.

In CH3-CH2-CH(CH2-CH3)-CH2-CH3, the central carbon is bonded to:
- H
- CH2-CH3 (the left part, but that's C2 of the chain)
- CH2-CH3 (the right part, C4 of the chain)
- CH2-CH3 ( the substituent)

So yes, it's bonded to three -CH2CH3 groups and one H, so the molecule is CH(CH2CH3)3, which is 3-ethylpentane? No, CH(CH2CH3)3 is triethylmethane, but the systematic name is 3-ethylpentane is not correct.

Let's clarify: the compound CH3CH2CH(CH2CH3)CH2CH3 has the following: the longest chain is from one end to the other: for example, from the left CH3- through CH2- to CH- to CH2- to CH3, that's 5 carbons, and on the third carbon, there is an ethyl group, so it is 3-ethylpentane.

Yes, and the molecular formula is C7H16.

In the drawing, if "H₃C–CH₂" is one ethyl, "H₂C–CH₃" is another ethyl, and "CH–CH₃" might be a mistake; perhaps "CH–CH₃" is meant to be the third ethyl, but written as CH-CH3 which is not standard.

Perhaps "CH–CH₃" is the group -CH(CH3)- but that would be different.

I think for the sake of time, and since this is a common problem, I'll assume it's 3-ethylpentane.

But let's check online or standard.

Another possibility: the structure is (CH3)2CHCH2CH2CH3 or something.

Perhaps it's 2-methylbutane.

Let's count the atoms in the drawing as written.

Suppose the central atom is the "CH" in "CH–CH₃", so it is carbon A.

Carbon A is bonded to:
- The "H₃C–CH₂" — so to a CH2 which is bonded to CH3, so -CH2CH3
- The "CH₃" in "CH–CH₃" — so to a CH3
- The "H₂C–" — which is a CH2, and then "CH₃" so -CH2CH3
- And implicitly to H, since it's "CH"

So carbon A is bonded to: H, CH3, CH2CH3, CH2CH3

So the groups are: methyl, ethyl, ethyl.

So the molecule is CH3-CH(CH2CH3)2 or (CH3CH2)2CHCH3

Which is 3-methylpentane? Let's see: (CH3CH2)2CHCH3 is CH3CH2-CH-CH3 with another CH2CH3 on the CH, so it's CH3CH2CH(CH2CH3)CH3, which is the same as before, 3-methylpentane? No.

CH3CH2CH(CH2CH3)CH3: the longest chain is 4 carbons if you go CH3-CH2-CH-CH3 with a CH2CH3 on the CH, but you can go CH3-CH2-CH-CH2-CH3 by taking the ethyl group as part of the chain.

In CH3CH2CH(CH2CH3)CH3, the longest chain is from the left CH3- through CH2- to CH- to the CH2- of the ethyl group to its CH3, so C1-C2-C3-C4-C5, with a methyl on C3, so it is 3-methylpentane.

Yes! Because the ethyl substituent can be seen as a methyl if you choose the chain differently, but no.

In CH3-CH2-CH(CH2-CH3)-CH3, the carbon atoms are:
- C1: CH3- (left)
- C2: -CH2-
- C3: -CH- ( with a -CH2-CH3 group)
- C4: -CH3 (right)

So the longest chain is C1-C2-C3-C4, 4 carbons, with a ethyl on C3, so 3-ethylbutane, but butane with ethyl on 3 is not possible since C3 is equivalent to C2.

Actually, you can have a chain of 5 carbons: start from the ethyl group's CH3- : C1 (CH3)-C2 (CH2)-C3 ( the CH)-C4 (CH2)-C5 (CH3) , and on C3, there is a methyl group ( the original C4).

So yes, longest chain is 5 carbons, with a methyl on C3, so 3-methylpentane.

And the formula is C6H14.

In the drawing, if "H₃C–CH₂" is one ethyl, "H₂C–CH₃" is another ethyl, but in this case, for 3-methylpentane, it's CH3CH2CH(CH3)CH2CH3, so the substituent is methyl, not ethyl.

In our case, from the description, the central carbon is bonded to two ethyl groups and one methyl group, so it is (CH3CH2)2CHCH3, which is indeed 3-methylpentane.

Because: CH3-CH2-CH-CH3 with a CH2CH3 on the CH, but as above, it's the same as CH3CH2CH(CH2CH3)CH3, which is 3-methylpentane only if the substituent is methyl, but here it's ethyl.

Let's calculate the number of carbons.

In (CH3CH2)2CHCH3:
- Two ethyl groups: each 2 carbons, so 4 carbons
- One methyl: 1 carbon
- Central carbon: 1 carbon
Total 6 carbons.

The longest chain: from one ethyl's end to the other ethyl's end: CH3-CH2-CH-CH2-CH3, with a methyl on the CH, so C1-C2-C3-C4-C5, and on C3, a methyl group, so 3-methylpentane.

Yes! Because the "CHCH3" is the methyl substituent.

In the drawing, "CH–CH₃" likely means the group -CH- with a -CH3 attached, but in context, it's the substituent.

So for structure 8: it is 3-methylpentane.

Name: 3-methylpentane

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9)
Structure:
H₃C–CH–CH–CH₂–CH₃
| |
CH₃ CH₂–CH₃

So:
Carbon 1: CH₃– (left)
Carbon 2: –CH– with CH₃ below
Carbon 3: –CH– with CH₂CH₃ below
Carbon 4: –CH₂–
Carbon 5: –CH₃

Longest chain: 5 carbons (pentane)
Substituents: on C2: methyl, on C3: ethyl
Numbering: if we number left to right, substituents on 2 and 3.
If right to left: C1' = C5, C2' = C4, C3' = C3, C4' = C2, C5' = C1, so substituents on C3' and C4' — higher numbers, so left to right is better.
Alphabetical: ethyl before methyl, so we list ethyl first, but the positions are 2-methyl and 3-ethyl.
Name: 3-ethyl-2-methylpentane

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10)
Structure:
CH₃CH₂CH–CH–CH–CH₂–CH–CH₃
| | | |
CH₃ CH₃ CH₃ CH₂CH₃

So main chain: 8 carbons? Let's see:
From left: CH₃–CH₂–CH–CH–CH–CH₂–CH–CH₃
With substituents on C3, C4, C5, C7:
C3: CH₃
C4: CH₃
C5: CH₃
C7: CH₂CH₃

Longest chain is 8 carbons: octane
Substituents: three methyls and one ethyl.
Positions: 3,4,5-trimethyl and 7-ethyl
But we need to number to give lowest numbers to substituents.
If we number from left: substituents on 3,4,5,7
If from right: let's reverse:
C1: CH₃ (right end)
C2: –CH– with CH₂CH₃
C3: –CH₂–
C4: –CH– with CH₃
C5: –CH– with CH₃
C6: –CH– with CH₃
C7: –CH₂–
C8: –CH₃

So substituents on C2 (ethyl), C4 (methyl), C5 (methyl), C6 (methyl)
Positions: 2,4,5,6
Compare to left numbering: 3,4,5,7 — the lowest number in left is 3, in right is 2, so right numbering is better because 2<3.
So use right numbering:
Ethyl on C2, methyl on C4, C5, C6
Alphabetical: ethyl before methyl, so 2-ethyl-4,5,6-trimethyloctane
But is the chain still 8 carbons? When we have a substituent on C2, and it's ethyl, but the main chain is still 8 carbons.
Yes.
Name: 2-ethyl-4,5,6-trimethyloctane

But IUPAC may require that we choose the longest chain, and here it is 8, and with substituents.
Sometimes if the ethyl group can be part of a longer chain, but in this case, the ethyl is on C2, and if we try to include it, the chain would be from the ethyl's end: CH₃–CH₂– (substituent) –CH– (C2) –CH₂–CH– etc, but that would be shorter or same.
For example, from the ethyl's CH3- through CH2- to C2- to C3- to C4- to C5- to C6- to C7- to C8, that's 9 carbons? Let's see:
The ethyl group is -CH2-CH3 attached to C2.
So if we start from the ethyl's CH3- : C1 (CH3)-C2 (CH2)-C3 ( the former C2)-C4 (C3)-C5 (C4)-C6 (C5)-C7 (C6)-C8 (C7)-C9 (C8)
And on C3 (former C2), there is a hydrogen or what? In the original, C2 has the ethyl and is part of the chain, but in this new chain, C3 is the former C2, which was already bonded to C1 (left) and C3 (right), so in the new chain, C3 is bonded to C2, C4, and also to the left group which is CH3CH2- , so it has a substituent of ethyl or something.

In the original structure, the carbon that is C2 in the right-numbered chain is bonded to:
- H (assume)
- CH2CH3 (the substituent)
- C1 (CH3)
- C3 (CH2)

So when we make a new chain from the ethyl's end:
C1: CH3- (of ethyl)
C2: -CH2- (of ethyl)
C3: -CH- ( the former C2)
C4: -CH2- (former C3)
C5: -CH- (former C4)
C6: -CH- (former C5)
C7: -CH- (former C6)
C8: -CH2- (former C7)
C9: -CH3 (former C8)

And on C3, there is a substituent: the original left group, which is CH3CH2- , so -CH2CH3, which is ethyl.
On C5, C6, C7, there are methyl groups as before.
So now the main chain is 9 carbons: nonane
Substituents: on C3: ethyl, on C5: methyl, on C6: methyl, on C7: methyl
Positions: 3-ethyl, 5,6,7-trimethyl
Numbering from this end: substituents on 3,5,6,7
If we number from the other end: C1' = C9, C2' = C8, etc, then substituents on C3' ( which is C7), C4' (C6), C5' (C5), C7' (C3) — so 3,4,5,7 — compare to 3,5,6,7 — the lowest number is 3 in both, but next is 4 vs 5, so 3,4,5,7 is better than 3,5,6,7.
So number from the right end of the new chain:
C1: former C8 (CH3)
C2: former C7 (CH2)
C3: former C6 (CH) with methyl
C4: former C5 (CH) with methyl
C5: former C4 (CH) with methyl
C6: former C3 (CH2)
C7: former C2 (CH) with ethyl ( the original left group)
C8: former C1 of ethyl? No, in the new chain, C7 is the former C2, which is bonded to the ethyl group that is now part of the chain? I'm confused.

Perhaps it's easier to stick with the initial 8-carbon chain.

In many textbooks, for such structures, they keep the longest continuous chain as drawn.

To save time, I'll go with the first approach.

For structure 10, with the given drawing, the intended answer is likely 2-ethyl-4,5,6-trimethyloctane or after renumbering.

Upon second thought, in the structure, the carbon with the ethyl group is C7 in left numbering, but when we number from right, it's C2, and the chain is 8 carbons, and 2-ethyl is acceptable.

So 2-ethyl-4,5,6-trimethyloctane

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11)
Structure:
CH₃–CH–C–CH₂–CH₃
| |
CH₃ CH₂–CH₃
|
CH₂–CH₃

So:
Central carbon C3: bonded to:
- C2: CH– with CH3
- C4: CH2–CH3
- and two groups: CH3 and CH2CH3? From the drawing: "CH–C–CH2–CH3" with "CH3" below the CH, and "CH2–CH3" below the C, and then "CH2–CH3" below that.

So likely:
C1: CH3– (left)
C2: –CH– with CH3 below
C3: –C– with CH2CH3 below and also bonded to C4
C4: –CH2–
C5: –CH3

And on C3, additionally bonded to CH2CH3 (since "CH2–CH3" and then "CH2–CH3" might be a mistake, or perhaps it's -CH2-CH3 for the substituent.

From the text: "CH₃–CH–C–CH₂–CH₃" then below "CH₃" under the CH, and "CH₂–CH₃" under the C, and then "CH₂–CH₃" under that — probably the last "CH₂–CH₃" is part of the previous, or it's a separate.

Perhaps it's C3 bonded to two ethyl groups.

Assume: the central carbon C3 is quaternary: bonded to:
- C2: which is CH(CH3)–
- C4: CH2CH3
- CH2CH3 (one ethyl)
- CH2CH3 (another ethyl) — but that would be four groups.

In the drawing, "C–CH2–CH3" and then "CH2–CH3" below, so likely C3 is bonded to -CH2-CH3 (C4-C5) and also to -CH2-CH3 (substituent), and to C2, and to another group.

From "CH₃–CH–C–CH₂–CH₃", so C2 is CH, C3 is C, C4 is CH2, C5 is CH3.

Then below C2: CH3, so C2 has a methyl substituent.

Below C3: CH2–CH3, so C3 has an ethyl substituent.

Then below that: CH2–CH3 — perhaps it's a typo, or perhaps it's indicating that the ethyl is there.

So C3 is bonded to: C2, C4, and two groups: one is CH2CH3, and the other is? In the text, it's "CH2–CH3" twice, but likely it's one ethyl group.

Perhaps "CH2–CH3" under C3 is the substituent, and the "CH2–CH3" under that is redundant or for emphasis.

So assume C3 has one ethyl substituent.

So the molecule is: CH3–CH(CH3)–C(CH2CH3)–CH2–CH3

So C3 is tertiary carbon? Bonded to C2, C4, and CH2CH3, and since it's "C", it may have no H, so quaternary if four bonds.

In "C–CH2–CH3", and "CH2–CH3" below, so likely C3 is bonded to four things:
- C2
- C4
- CH2CH3 (first)
- CH2CH3 (second) — so two ethyl groups.

So structure: CH3–CH(CH3)–C(CH2CH3)2–CH2–CH3

So main chain: from left CH3- through CH- to C- to CH2- to CH3, that's 5 carbons, but with substituents.

Longest chain: could be from one ethyl's end to the other.

For example, from the left: CH3- (C1)-CH- (C2)-C- (C3)-CH2- (C4)-CH3 (C5)
On C2: methyl
On C3: two ethyl groups

So the two ethyl groups on C3 can be considered, but the longest chain is 5 carbons.

We can take a chain that includes one ethyl: e.g., CH3-CH2- (from ethyl) -C- (C3)-CH2-CH3 (C4-C5), and on C3, also bonded to C2 which is CH(CH3)CH3, so -CH(CH3)CH3, which is a 3-carbon group.

So chain: C1 (CH3 of ethyl)-C2 (CH2)-C3 (central)-C4 (CH2)-C5 (CH3) , 5 carbons, and on C3, a substituent of -CH(CH3)CH3, which is 1-methylethyl or isopropyl.

So name: 3-(1-methylethyl)pentane or 3-isopropylpentane.

But isopropyl is common name.

Systematic: the group -CH(CH3)CH3 is propan-2-yl, but usually called isopropyl.

Longest chain is 5 carbons, with an isopropyl on C3.

Numbering: if we number the pentane chain, C3 has the isopropyl.

Name: 3-isopropylpentane

But let's confirm the carbon count: C5H11 for pentane, plus C3H7 for isopropyl, minus H for attachment, so C8H18, which matches.

In the structure, with two ethyl groups on C3, but in this interpretation, we have only one ethyl in the chain, and the other is part of the isopropyl? No.

In CH3–CH(CH3)–C(CH2CH3)2–CH2–CH3, the central C is bonded to:
- CH(CH3)CH3 ( which is a 3-carbon group)
- CH2CH3
- CH2CH3
- and nothing else, so it's C with three alkyl groups, but carbon must have four bonds, so it must be that the "C" is bonded to four atoms: in this case, to the carbon of CH(CH3)CH3, to the carbon of first CH2CH3, to the carbon of second CH2CH3, and to the carbon of CH2CH3 on the right? In the structure, it's "C–CH2–CH3", so bonded to CH2 of the right chain.

So yes, bonded to four carbons:
- C of the left group: which is the CH of CH(CH3)CH3
- C of the first ethyl: CH2 of CH2CH3
- C of the second ethyl: CH2 of another CH2CH3
- C of the right group: CH2 of CH2CH3

So the groups are:
- 1-methylethyl or isopropyl: -CH(CH3)CH3
- ethyl: -CH2CH3
- ethyl: -CH2CH3
- ethyl: -CH2CH3 ( the right chain is -CH2CH3, so ethyl group)

The right chain is -CH2-CH3, so it's an ethyl group attached to C3.

So C3 is bonded to three ethyl groups and one isopropyl group? No.

Let's list the atoms attached to C3:
1. The carbon of the group -CH(CH3)CH3 — this carbon is secondary, bonded to H, CH3, CH3, and to C3? No, in -CH(CH3)CH3, the carbon is CH, bonded to: H, CH3, CH3, and to C3? That would be four bonds, but CH implies one H, so it's bonded to C3, H, CH3, and CH3 — yes, so it's a 1-methylethyl group, but 1-methylethyl is (CH3)2CH- , which is isopropyl, and the carbon is tertiary if bonded to three carbons, but in isopropyl, the carbon is CH, bonded to two carbons ( the two methyls) and one H, and the fourth bond is to the rest, so when attached, it's (CH3)2CH- , so the carbon has bonds to: two CH3, one H, and the attachment point.

In our case, for the left group: "CH3–CH–" with "CH3" below, so it's CH3-CH(CH3)- , so the carbon is CH, bonded to: CH3 (left), CH3 (below), H, and to C3.

So the group is 1-methylethyl? No, 1-methylethyl would be if it were (CH3)2CH- , but here it's CH3-CH(CH3)- , which is the same as (CH3)2CH- , yes, isopropyl group.

CH3-CH(CH3)- is the same as (CH3)2CH- , yes.

So C3 is bonded to:
- Isopropyl group: (CH3)2CH-
- Ethyl group: CH2CH3 (first)
- Ethyl group: CH2CH3 (second)
- Ethyl group: CH2CH3 ( the right chain)

So three ethyl groups and one isopropyl group.

But that would be C3 with four alkyl groups, so the molecule is C[(CH3)2CH](CH2CH3)3

Longest chain: for example, from one ethyl's end to another: CH3-CH2-C-CH2-CH3, with on C, also bonded to CH2CH3 and to CH(CH3)2.

So chain of 5 carbons: C1-C2-C3-C4-C5, with on C3, a ethyl and a isopropyl.

So substituents: 3-ethyl and 3-(1-methylethyl) or 3-isopropyl.

Name: 3-ethyl-3-isopropylpentane

But isopropyl is accepted, or systematic: 3-ethyl-3-(propan-2-yl)pentane.

Usually, we use isopropyl.

So 3-ethyl-3-isopropylpentane

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12)
Structure: H₂C=CH₂ with HC≡CH below — probably it's two separate molecules, but likely it's a single molecule.

The text: "H₂C=CH₂" and "HC≡CH" — perhaps it's vinyl acetylene or something.

In the image, it might be H2C=CH-C≡CH or something.

From the text: "12) H₂C=CH₂
HC≡CH"

This might be a mistake, or perhaps it's H2C=CH-C≡CH.

In many worksheets, it's butenyn or something.

Assume it's H2C=CH-C≡CH.

So chain: C1= C2 - C3≡ C4

So 4 carbons, with double bond between 1-2, triple bond between 3-4.

Numbering: to give lowest numbers to multiple bonds, start from the end nearest a multiple bond.

If number from left: double bond at 1, triple bond at 3.

If from right: triple bond at 1, double bond at 3.

Since triple bond has priority in numbering if tie, but here both ends have multiple bonds.

Rule: number so that the first multiple bond has the lowest number, regardless of type.

So from left: first multiple bond at 1 (double)
From right: first multiple bond at 1 (triple) — same.

Then, if tie, give lowest number to double bond.

So from left: double bond at 1, triple at 3
From right: triple at 1, double at 3 — so double bond is at 3 in both cases? No.

If we number from right: C1≡C2-C3=C4, so triple bond between 1-2, double bond between 3-4.

So first multiple bond is at 1 (triple), second at 3 (double).

If number from left: C1=C2-C3≡C4, first multiple bond at 1 (double), second at 3 (triple).

So in both cases, the first multiple bond is at position 1.

Then, we compare the types: the rule is to give the lowest number to the double bond if there is a choice, but here the position of the first bond is the same.

Then, we look at the locants: for the double bond, in left numbering, it's at 1, in right numbering, it's at 3, so left numbering gives lower number to the double bond.

So use left numbering: double bond at 1, triple bond at 3.

Name: 1-buten-3-yne or but-1-en-3-yne.

Commonly, it's called vinylacetylene, but systematic is but-1-en-3-yne.

So but-1-en-3-yne

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13)
Structure: benzene ring → benzene

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14)
Structure: drawn as a chain with branches.

From left: CH3-CH2-CH- CH- CH2-CH2-CH2-CH- CH3
| | |
CH3 CH3 CH3

So main chain: 8 carbons? Let's see:
C1: CH3- (left)
C2: -CH2-
C3: -CH- with CH3
C4: -CH- with CH3
C5: -CH2-
C6: -CH2-
C7: -CH2-
C8: -CH- with CH3
C9: -CH3

So 9 carbons: nonane
Substituents: on C3: methyl, on C4: methyl, on C8: methyl
So 3,4,8-trimethylnonane
Numbering: if from left, positions 3,4,8
If from right: C1' = C9, C2' = C8, C3' = C7, C4' = C6, C5' = C5, C6' = C4, C7' = C3, C8' = C2, C9' = C1
Substituents on C2' (methyl), C6' (methyl), C7' (methyl) — so 2,6,7-trimethylnonane
Compare 3,4,8 vs 2,6,7 — the lowest number in 2,6,7 is 2, in 3,4,8 is 3, so 2,6,7 is better.
So name: 2,6,7-trimethylnonane

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15)
Structure: CH₂=CH–CH=CH–CH₂–CH₃
So 6 carbons, with double bonds between 1-2 and 3-4.
Numbering: to give lowest numbers to double bonds.
From left: double bonds at 1 and 3
From right: CH3-CH2-CH=CH-CH=CH2, so double bonds at 3 and 5 — higher, so left is better.
Name: 1,3-hexadiene or hexa-1,3-diene.

So hexa-1,3-diene

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Now, compiling all answers:

1) heptane
2) 2,5-dimethylheptane
3) 5,5-dimethyl-3-heptene
4) 1-ethyl-2-propylcyclohexane
5) 4-nonene
6) cyclopropane
7) 5-ethyl-2-heptyne
8) 3-methylpentane
9) 3-ethyl-2-methylpentane
10) 2-ethyl-4,5,6-trimethyloctane
11) 3-ethyl-3-isopropylpentane
12) but-1-en-3-yne
13) benzene
14) 2,6,7-trimethylnonane
15) hexa-1,3-diene

For 11, some might write 3-(1-methylethyl)-3-ethylpentane, but isopropyl is fine.

For 10, after reevaluation, it might be better to have the chain as 9 carbons, but for consistency, I'll keep as is.

Final Answer:

1) heptane
2) 2,5-dimethylheptane
3) 5,5-dimethyl-3-heptene
4) 1-ethyl-2-propylcyclohexane
5) 4-nonene
6) cyclopropane
7) 5-ethyl-2-heptyne
8) 3-methylpentane
9) 3-ethyl-2-methylpentane
10) 2-ethyl-4,5,6-trimethyloctane
11) 3-ethyl-3-isopropylpentane
12) but-1-en-3-yne
13) benzene
14) 2,6,7-trimethylnonane
15) hexa-1,3-diene