Ch. 14 – Conjugation, Resonance, Dienes Flashcards
What is conjugation? What does it allow in terms of electrons?
the overlap of p orbitals on 3 or more adjacent carbons
allows electrons to delocalize and makes molecule more stable
What are 1,3-dienes?
have two double bonds separated by one single bond (conjugated)
What is the hybridization of all carbons in 1,3-dienes?
all carbons are sp2
In conjugated systems, how do bond lengths change for double and single bonds?
double bonds = longer than normal
single bonds = shorter than normal
due to resonance
Which is better res structure: has more charges or has less charges?
has less charges
What makes the better res structure: has atoms without full octets or max number of carbons have full octet?
max number of carbons have full octet
What makes a better res structure: negative charge on more EN atoms, negative charge on less EN atoms?
negative charge on more EN atoms
What makes a resonance structure a major contributor to the resonance hybrid?
the better (more stable) resonance structure will be major contributor
What is the hybridization of a carbon with a lone pair adjacent to a carbon with a double bond?
sp2
What are polyenes?
compounds with many pi bonds
What is resonance energy?
difference in energy between WHAT due to stabilization of a molecule because of conjugation
Which has a more exothermic (more negative) ∆Hº? 1,4-diene or 1,3-diene?
1,4-diene because 1,3-diene is conjugated and is lower energy so it thus releases less energy
What type of wavelengths (of max absorbance) do conjugated dienes absorb and does it thus take a lot of energy to excite these?
longer wavelengths
takes less energy to excite
What product does electrophilic addition of an isolated diene give (for 1 eq)?
one markovnikov product
What happens in hydrobromination of 1,3-dienes?
1,3-diene reacts with HBr to form 1,2 or 1,4 addition product
