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condensed structures

I am currently working on an assignment and I am confused about what kind of hybridisation exists for the first condensed structure CH3CN. Does the CH3 have sp2 hybridisation? I suspect its that because it has 3 hydrogens (1s^2) and 1 carbon (1s^2 2s^2 2p^2), allowing for 3 sigma bonds and 1 pi bond. I believe that the C standing alone would have sp3 because it looks like a bent shape? I am not too sure. Thank you.

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    $\begingroup$ CH3CN is not a bent molecule as drawn. $\endgroup$
    – matt_black
    Commented Aug 8, 2023 at 10:29
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    $\begingroup$ Should be straight. $\endgroup$
    – WChan
    Commented Aug 9, 2023 at 4:48

2 Answers 2

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In $\ce{CH3CN}$, the three atoms $\ce{C,C}$ and $\ce{N}$ are alined. The terminal $\ce{C}$ atom (in $\ce{CH3}$) is hybridized sp3. The central $\ce{C}$ atom is hybridized sp. The bond $\ce{C-C}$ between $\ce{CH3}$ and $\ce{CN}$ is sigma, and the bond $\ce{CN}$ has one sigma and two pi bonds.

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  • $\begingroup$ Hi! Is the terminal C atom hybridised sp3 becuse its a tetrahedral shape? Or is there another way to understand why? Like how the hydrogen atoms are all single bonded to the carbon to create 3 sp3 hybrid orbitals? I'm trying to understand why. Thank you! $\endgroup$
    – WChan
    Commented Aug 8, 2023 at 6:29
  • $\begingroup$ When $\ce{C}$ is linked to 4 atoms, it is hybridized sp3, and the bonds are all sigma. When $\ce{C}$ is linked to only 3 atoms, it is hybridized sp2, with three sigma bonds, and there is somewhere a pi bond. When $\ce{C}$ is linked to 2 atoms, it is hybridized sp and there are two pi bonds. $\endgroup$
    – Maurice
    Commented Aug 8, 2023 at 7:55
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As Maurice said, the first carbon is sp3 and the second one is sp.

The easiest way to understand why is not to look at the shape (but the other way around - by knowing hybridization you determine shape), but at the number of atoms bonded on carbon. To bond 2 atoms together you need a sigma bond. If carbon has 4 atoms bonded on it, then it has 4 sigma bonds and is thus sp3 hybridized. If it has 3 atoms bonded, then it has 3 sigma bonds and one pi bond, and is sp2 hybridized. If it has only 2 atoms bound then it has 2 sigma bonds and 2 pi bonds, and is sp hybridized.

When you know the hybridization it is easy to determine the bond angles and shapes. Tetrahedral shape has 109.5° angles is typical for sp3 hybridization, sp2 has 120° angles and sp has 180° angles and linear shape.

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