Question

how many $\sigma$ and $\pi$ bonds are in this molecule?
molecular structure diagram
number of $\sigma$ bonds:

Explanation:

Step1: Identify single bonds (σ bonds)

Single bonds are all σ bonds. Let's count each single bond:
- C-H bonds: First C has 2 H, second C has 1 H, last C has 1 H. So 2 + 1 + 1 = 4 C-H σ bonds.
- C-C single bonds: Between second and third C, third and fourth C. So 2 C-C σ bonds.
- C-O bond: Third C and O, 1 σ bond.
- Now, also, in double bonds (C=C, C=O) and triple bond (C≡C), the first bond is σ. Let's handle those:
- C=C (first double bond): 1 σ bond.
- C=O (carbonyl): 1 σ bond.
- C≡C (triple bond): 1 σ bond.
- Also, count the single bonds within the structure:
- First C: 2 C-H (σ), 1 C=C (σ part) → wait, maybe better to list all bonds:
- Bonds:
- C1 (leftmost) to H: 2 (σ)
- C1 to C2: double bond (1 σ, 1 π)
- C2 to H: 1 (σ)
- C2 to C3: single bond (σ)
- C3 to O: double bond (1 σ, 1 π)
- C3 to C4: single bond (σ)
- C4 to C5: triple bond (1 σ, 2 π)
- C5 to H: 1 (σ)
- Now count σ bonds:
- C1-H: 2
- C1-C2 (σ in double bond): 1
- C2-H: 1
- C2-C3: 1
- C3-O (σ in double bond): 1
- C3-C4: 1
- C4-C5 (σ in triple bond): 1
- C5-H: 1
- Wait, did we miss any? Let's list all atoms:
- C1: bonded to 2 H, 1 C2 (double bond) → σ bonds: 2 (H) + 1 (C2) = 3
- C2: bonded to 1 H, 1 C1 (double bond), 1 C3 (single bond) → σ bonds: 1 (H) + 1 (C1) + 1 (C3) = 3
- C3: bonded to 1 O (double bond), 1 C2 (single bond), 1 C4 (single bond) → σ bonds: 1 (O) + 1 (C2) + 1 (C4) = 3
- C4: bonded to 1 C3 (single bond), 1 C5 (triple bond) → σ bonds: 1 (C3) + 1 (C5) = 2
- C5: bonded to 1 C4 (triple bond), 1 H → σ bonds: 1 (C4) + 1 (H) = 2
- O: bonded to C3 (double bond, σ part) → 1 σ
- H atoms: 2 (C1) + 1 (C2) + 1 (C5) = 4 H, each with 1 σ bond to C.
- Wait, maybe my initial approach was wrong. Let's count all σ bonds:
- Single bonds (all σ):
- C1-H: 2
- C2-H: 1
- C2-C3: 1
- C3-C4: 1
- C5-H: 1
- σ bonds in multiple bonds (double and triple, first bond is σ):
- C1-C2 (double bond): 1
- C3-O (double bond): 1
- C4-C5 (triple bond): 1
- Now sum these:
- Single σ bonds: 2 + 1 + 1 + 1 + 1 = 6
- σ in multiple bonds: 1 + 1 + 1 = 3
- Total: 6 + 3 = 9? Wait, no, let's list each bond:
1. C1-H (1)
2. C1-H (2)
3. C1-C2 (σ)
4. C2-H
5. C2-C3
6. C3-O (σ)
7. C3-C4
8. C4-C5 (σ)
9. C5-H
Wait, that's 9? No, wait, C3 has a double bond with O, so C3-O is 1 σ. C4-C5 is triple, 1 σ. C1-C2 is double, 1 σ. Then the single bonds: C1-H (2), C2-H (1), C2-C3 (1), C3-C4 (1), C5-H (1). So single bonds: 2 + 1 + 1 + 1 + 1 = 6. Multiple bond σ: 1 (C1-C2) + 1 (C3-O) + 1 (C4-C5) = 3. Total σ: 6 + 3 = 9? Wait, no, maybe I missed a bond. Wait, the structure is:

Let's draw the structure with atoms:

C1 (H2C=) bonded to C2 (=CH-) bonded to C3 (-C(=O)-) bonded to C4 (-C≡C-) bonded to C5 (-H)

So atoms:

C1: H, H, C2 (double)
C2: H, C1 (double), C3 (single)
C3: O (double), C2 (single), C4 (single)
C4: C3 (single), C5 (triple)
C5: C4 (triple), H

Now count σ bonds:

- C1-H: 2 (σ)
- C1-C2: 1 (σ, part of double bond)
- C2-H: 1 (σ)
- C2-C3: 1 (σ)
- C3-O: 1 (σ, part of double bond)
- C3-C4: 1 (σ)
- C4-C5: 1 (σ, part of triple bond)
- C5-H: 1 (σ)

Now sum these: 2 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = Wait, 2 (C1-H) +1 (C1-C2) +1 (C2-H) +1 (C2-C3) +1 (C3-O) +1 (C3-C4) +1 (C4-C5) +1 (C5-H) = 2+1=3, +1=4, +1=5, +1=6, +1=7, +1=8, +1=9? Wait, no, C3 has a double bond with O, so that's 1 σ. C4 has a triple bond with C5, 1 σ. C1 has a double bond with C2, 1 σ. Then the single bonds: C1-H (2), C2-H (1), C2-C3 (1), C3-C4 (1), C5-H (1). So 2+1+1+1+1=6 single σ, plus 3 from multiple bonds (1+1+1), total 9. Wait, but maybe I made a mistake. Let's check again.

Alternatively, another method: each single bond is 1 σ, each double bond has 1 σ and 1 π, each triple bond has 1 σ and 2 π.

Let's list all bonds:

- Single bonds (σ):
- C-H: let's count all C-H bonds: C1 has 2, C2 has 1, C5 has 1. Total C-H: 4. Each is σ.
- C-C single bonds: C2-C3, C3-C4. 2 bonds, each σ.
- Double bonds (each has 1 σ, 1 π):
- C1-C2 (double), C3-O (double). 2 double bonds, so 2 σ.
- Triple bond (has 1 σ, 2 π):
- C4-C5 (triple). 1 σ.

Now sum σ bonds:

C-H: 4

C-C single: 2

Double bond σ: 2

Triple bond σ: 1

Total: 4 + 2 + 2 + 1 = 9? Wait, 4+2=6, +2=8, +1=9. Yes, that matches. Wait, but let's count again:

C-H bonds: C1 (2), C2 (1), C5 (1) → 4. Correct.

C-C single bonds: C2-C3, C3-C4 → 2. Correct.

Double bonds: C1-C2 (double), C3-O (double) → 2 double bonds, each contributes 1 σ → 2. Correct.

Triple bond: C4-C5 (triple) → 1 σ. Correct.

So total σ bonds: 4 + 2 + 2 + 1 = 9? Wait, no, wait: C1-C2 is a double bond (σ and π), C3-O is a double bond (σ and π), C4-C5 is a triple bond (σ and 2 π). Then the single bonds: C-H (4), C-C single (2). Then the σ from double and triple: 1 (C1-C2) + 1 (C3-O) + 1 (C4-C5) = 3. Then single σ: 4 + 2 = 6. Total: 6 + 3 = 9. Yes, that's correct.

Step2: Wait, maybe I missed a bond? Let's check the structure again. The structure is:

H H
| |
C = C - C = O - C ≡ C - H
|
H? Wait, no, the original structure: first C has two H, second C has one H, third C is carbonyl (C=O), fourth C, fifth C with one H. Wait, maybe the second C (C2) has one H, C1 has two H, C5 has one H. So C-H bonds: 2 (C1) + 1 (C2) + 1 (C5) = 4. Correct.

C-C bonds: C1-C2 (double), C2-C3 (single), C3-C4 (single), C4-C5 (triple). So single C-C bonds: C2-C3, C3-C4 → 2. Correct.

Double bonds: C1-C2, C3-O → 2. Each has 1 σ.

Triple bond: C4-C5 → 1 σ.

So σ bonds:

C-H: 4

C-C single: 2

Double bond σ: 2

Triple bond σ: 1

Total: 4 + 2 + 2 + 1 = 9? Wait, no, 4 (C-H) + 2 (C-C single) + 2 (double σ) + 1 (triple σ) = 9. Yes. Wait, but let's count each bond:

1. C1-H (σ)
2. C1-H (σ)
3. C1-C2 (σ)
4. C2-H (σ)
5. C2-C3 (σ)
6. C3-O (σ)
7. C3-C4 (σ)
8. C4-C5 (σ)
9. C5-H (σ)

Wait, that's 9 bonds? Wait, no, C3-O is a double bond, so that's one σ. C4-C5 is triple, one σ. C1-C2 is double, one σ. Then the single bonds: C1-H (2), C2-H (1), C2-C3 (1), C3-C4 (1), C5-H (1). So 2+1+1+1+1=6 single σ, plus 3 from multiple bonds (1+1+1), total 9. Yes, that's correct.

Answer:

9