Alkenes - Properties of the Alkenes Flashcards
(9 cards)
What is a pi bond?
- A bond formed by the sideways overlap of 2 p-orbitals.
- Electron density is above & below the plane of the bonding atoms.
How many sigma bonds & pi bonds are there in a double bond?
There is 1 sigma bond & 1 pi bond.
Describe & explain the arrangement of bonds around each C atom in an alkene.
- Each C atom (involved in the double bond) forms 3 single bonds, with H atoms/C atoms, and 1 double bond with the adjacent C atom.
- 3 single bonds arranged in a trigonal planar geometry, lying in a single plane with bond angles of 120°.
- Trigonal planar arrangement of the bonds is due to the equal repulsion between the bonding pairs of electrons.
Explain the high reactivity of alkenes.
Due to 3 key features of the pi bond in the C=C double bond:
- Its high electron density makes the pi-electrons highly accessible for reactions.
- Its protruding shape allows electrophiles to readily attack the pi-electrons.
- Its lower bond enthalpy requires less energy to break compared to sigma bonds.
Why is rotation restricted around the C=C double bond of alkenes?
The pi bond formed by the sideways overlap of the p-orbitals on the C atoms locks the C’s in position & prevents rotation around the double bond.
Why do alkenes undergo addition reactions?
They are unsaturated molecules - a molecule can add across the C=C double bond to forms a single saturated compound.
Explain whether alkenes react with electrophiles or nucleuphiles.
Electrophiles because there is an area of high electron density around the C=C double bond.
What is the difference between a sigma bond & a pi bond in terms of orbital overlap?
- Sigma bonds result from head-on overlap of atomic orbitals.
- Pi bonds result from sideways overlap of p-orbitals.
What is the general formula for cyclic alkenes?
CnH2n-2
