11. Alkanes Flashcards
Alkane
-saturated hydrocarbon whose carbon atoms are arranged in a chain
-maximum number of hydrogens on each carbon
-C atoms are tetrahedral (109.5°)
-ALIPHATIC HYDROCARBONS: physical properties of the higher members of this class resemble those of the long carbon-chain molecules in animal fats and plant oils
Hydrocarbon
-compound that contains only carbon and hydrogen atoms
•alkanes (single bond C-C)
•alkenes (double bond)
•alkynes (triple bond)
•arenes (one or more benzene-like rings)
Saturated hydrocarbon
-hydrocarbon that contains only C-C single bonds
Unsaturated hydrocarbon
-hydrocarbon that contains one or more C-C double/ triple bonds or benzene ring
Line-angle formula
-Abbreviated way to draw structural formulas in which each vertex and line terminus represents a carbon atom and each line represents a bond
Constitutional isomers
aka
Structural isomers
-compounds with the same molecular formula but a different connectivity of their atoms
-i.e. butane and 2-methylpropane
International Union of Pure and Applied Chemistry (IUPAC) system
NAMING ALKANE
•for unbranched alkane
1. Prefix: number of carbon atoms in chain
2. Suffix -ane
•for branched alkane
1. Take the longest chain as parent chain and its name becomes the root name
- Name and number each substituent on parent chain. Use hypen to connect number to name
2-Methylpropane - If there is one substituent, number the parent chain from the end that gives the substituent the lower number
2-Methylpentane NOT 4-Methylpentane - If same substituent occurs more than once, number the parent chain from the end that gives the lower number to the substituent encountered first. Use appropriate prefix (i.e. di-, tri-, tetra-). Use comma to separate number
2,4-Dimethylhexane - If two or more different substituent, list in alphabetical order and number the chain that gives lower number to first substituent encountered.
If equivalent positions, give the substituent of lower alphabetical the lower number
3-Ethyl-5-methylheptane NOT 3-Methyl-5-ethylheptane - Do not include prefixes or hypenated prefixes (sec-, tert-) in alphabetizing
4-Ethyl-2,2-dimethylhexane
Prefix
Meth
Eth
Prop
But
Pent
Hex
Hept
Oct
Non
Dec
Undec
Dodec
Tridec
Tetradec
Pentadec
Hexadec
Heptadec
Octadec
Nonadec
Eicos
Alkyl group
-group derived by removing a hydrogen from an alkane; symbol
—R
-named by dropping -ane from the name of parent alkane and add -yl
-prefix sec- (abbv secondary): carbon bonded to two other carbons
-prefix tert- (abbv tertiary): carbon bonded to three other carbons
Common names
-total number of carbon atoms , regardless of arrangement, determines the name
Cycloalkane
-saturated hydrocarbon that contains carbon atoms bonded to form a ring
•Naming:
1. Prefix the corresponding open-chain alkane with cyclo- and name substituents
2. No need to number if one substituent. If more than one, number the ring beginning the substituent of lower alphabetical order
Conformation
-any three-dimensional arrangement of atoms on a molecule that results from rotation about a single bond
Conformation
ALKANE
-majority of molecules in any alkane sample will be in the LEAST CROWDED CONFORMATION
-fewest will be in MOST CROWDED CONFORMATION
Conformation
CYCLOALKANE (CYCLOPENTANE)
-ENVELOPE CONFORMATION (most stable): 4 carbons are in a plane and the 5th carbon is bent out of the place (like an envelope flap)
-bond angle 109.5°
Conformation
CYCLOALKANE (CYCLOHEXANE)
-CHAIR CONFORMATION (most stable): 12 C-H bonds are arranged in two different orientations:
•Equatorial position- extends from the ring roughly perpendicular to imaginary axis of the ring
-if axial bond upward, equatorial slightly down vice versa
-alternating per carbon
•Axial position- extends from the ring parallel to the imaginary axis of the ring
-109.5°
-cyclohexane more stable if maximum number of substituent groups are EQUATORIAL
