Chapter 3

Unsaturation Recall: pentane – C 5 H 12 We refer to pentane as a saturated compound because the carbon atoms have the maximum number of possible substituents cyclopentane – C 5 H 10 We refer to cyclopentane as an unsaturated compound because the carbon atoms do not have the maximum number of possible substituents Can you think of any other ways to make an unsaturated molecule?

Double & Triple Bonds C 5 H 10 C5H8C5H8 C5H8C5H8 C 5 H 12 0° of unsaturation Degree of unsaturation = (# of double bonds) + (2 × # of triple bonds) + (# of rings) 1° of unsaturation2° of unsaturation Multiple sites of unsaturation:

Double & Triple Bonds C 5 H 10 C5H8C5H8 C5H8C5H8 C 5 H 12 0° of unsaturation Degree of unsaturation = (# of double bonds) + (2 × # of triple bonds) + (# of rings) 1° of unsaturation2° of unsaturation C n H 2×n+2 CnHnCnHn C n H 2×n-2

Double & Triple Bonds C 5 H 10 C5H8C5H8 C5H8C5H8 C 5 H 12 0° of unsaturation1° of unsaturation2° of unsaturation Degree of unsaturation = [2 + (2 x #Cs) + #Ns - #Hs - #Halogens]/2 C n H 2×n+2 CnHnCnHn C n H 2×n-2 C 6 H 10 BrCl C 8 H 10 NOBr 1° 4°

Double & Triple Bonds AlkenesAlkynes C 5 H 10 C5H8C5H8 C5H8C5H8 Alkanes C 5 H 12 pentane (n-pentane) 1-pentene How do we name these guys? 2-pentene 1-pentyne 2-pentyne

Rules for Naming Alkenes and Alkynes 1) Find the longest carbon chain containing the multiple bond 2) Start numbering from the end closest to the multiple bond 3) Finish as if you were naming an alkane only use the appropriate suffix (e.g., -ene for a double bond, -yne for a triple bond) Let’s try a practice problem

Name That Organic Compound pentene 1-3,4-dimethyl-

Name That Organic Compound 1,3-pentadiene

Nomenclature of Alkenes Common Terms You Should Know: vinylic carbons allylic carbons vinyl group allyl group 2-pentene allyl-4-vinyl-decane Alkenes are also called olefins.

Alkene Factoids Recall: rotate butane (n-butane) Now let’s look at 2-butene

Alkene Factoids The barrier to rotation is very large. This leads to the possibility of cis and trans isomers, stable, separable compounds with different properties.

E,Z Nomenclature (The higher the molcular weight, the higher the priority) Sometimes cis and trans are ambiguous; in such cases we resort to the more formal E,Z nomenclature. cis or trans? Z if highest priority substituents on same side of double bond E if highest priority substituents on opposite side of double bond A way to remember: Ecross, Zame Zide Look at each carbon atom and assign each group a priority

Practice (Z)-2-iodo-2-pentene 1,1-dibromo-1-propene

Practice