unit 4 - alkanes Flashcards
What is the notation for a straight alkane
what is the general formula
- also know as aliphatic compounds
- linear alkanes are called either straight- chain or normal (n-)
- CnH2n+2
Alkyl Groups
what are the other groups to memorize?
5 of them
- isopropyl
- isobutyl
- isoalkane
- sec-butyl
- tert-butyl
Nomenclature
How to name an alkane?
- longest carbon chain
- numbers of substituents have a branch at the lowest possible number
- identify and number the substituents
- list substituents in alphabetical order
- add prefixes like di- tri- etc. to multiple of the same substituent
Nomenclature
How to name an alkyl halide?
- similar to alkane
- longest cc chain
- lowest number for substituents; alkyl and halo groups have equal prority
Nomenclature
How to name alcohols?
- longest C chain containing th -OH group
- -OH group has the lowest number
- -ane -> -anol
- don’t forget to add prefixes if there is multiple
Nomenclature
How to name an alkene?
- general formula: CnH2n
- olefins, alkenyl or vinyl
1. Longest chain with C=C
2. give C=C lowest possible number
3. start nearest the first branch point
4. multiple bonds indicated with the suffix eg. -diene
5. OH group gets priority
Nomenclature
how to name a cycloalkene?
- numbering at the double bond and giving the substituents the lowest possible number
- cyclo as a prefix
Nomenclature
Some trivial alkenes as substituents to memeorize:
4 of them
- methylene group
- vinyl group (ethenyl)
- allul group (2-propenyl)
- cis-1-propenyl
Nomenclature
How to name alkynes?
- suffix is -yne
- similar with alkene
Chemistry of alkanes
Describe the synthesis of alkanes
define: saturated, unsaturated, hydrogenation
- alkene/alkyne -> alkene = hydrogenation
- alkene/alkyne are unsaturated
- alkene is saturated
Explain Conformational isomers
- rotation about single bonds
- sp3-sp3 single bonds are flexible, rotation can occur
- acyclic alkanes normally interconvert rapidly and therefor can’t be separated from each other
Describe Torsional strain and steric strain
- overlapping of bonds
- energy penalty resulting from the eclipsing of bonds
- high in energy
- seen in butane: eclipse
- repulsive interaction that results when two groups are forced together than their size allows
Nomenclature
Cycloalkanes - how to name as alkane or cycloalkane?
- count C in ring and any linear chain and compare length; whichever is larger is the parent
1. number ring so that branch points have the lowest number
2. alphabetic order of funcitonal groups
draw a cyclohexane chair conformer
describe stability if there was a substituent and explain the twist boat
- conformationally flexible at room temp
- twist boat is higher in energy; 12 H are eclipsed
- substituent more stable in equatorial than axial
