8.7 Alkynes and Cycloalkanes Flashcards
what are alkynes
Alkynes are unsaturated hydrocarbons containing at least one carbon-to-carbon triple bond.
what is the formula for alkynes
They have the general formula CnH2n-2when 1 triple bond is present.
what is the simplest alkyne
The simplest alkyne is ethyne, commonly known as acetylene. It is used as fuel in oxyacetylene welding torches. The molecular formula for ethyne is C2H2.
what is important about triple bonds
The triple bond is stronger and shorter than the double bond of an alkene and the single bond of an alkane. Triple bonds are even more reactive than either single bonds or double bonds. Atoms cannot rotate around a triple bond
what is important for naming alkynes
The names of the alkynes all end in ¨yne¨: ethyne, propyne, butyne, etc. Alkynes are named in the same way as alkenes. However, there are no cis or trans isomers among the alkynes because the molecules are always linear
how do you draw structure
Drawing structures works similarly to naming, except that they are the reverse of each other
what are cyclic alkanes / cycloalkanes
Cyclic Alkanes are like alkanes, but the end connects to the start forming a continues loop
what is the simplest cyclic hydrocarbon
The simplest cyclic hydrocarbon is cyclopropane, C3H6. A minimum of three carbons are required to form a ring. it is drawn triangular
how can you represent cyclic alkanes
Rings can be represented by a shorthand outline. Each corner represents a carbon atom. Any free bonds are filled with hydrogen atoms, unless otherwise indicated.
what is important to remember for naming cycloalkanes
Naming for cycloalkanes is similar to the others, though it is hard to know where to start numbering.
which is the first carbon when there is one substitution group in a cyclic alkane
If a cyclic alkane has only one substitution group, then the carbon which holds that substitution group automatically becomes carbon 1
how do you number the carbons when there are multiple substitution groups
If more than one carbon in the ring holds a substitution group, then there will always be two options for numbering the carbons, clockwise and counter clockwise.
Pick either carbon that holds a substitution group to be carbon 1, and then number the carbons in both directions. The correct numbering system will be the one in which the lowest sum of carbon locating numbers is used.
If one group is bigger than other, chose that as carbon 1
how do you list substitution groups
the substitution groups are listed in alphabetical order (ie. fluoro before methyl) -the prefixes di, tri, tetra etc. used to show several groups of the same kind are NOT considered when alphabetizing
what are benzene rings
A benzene ring is similar to cyclohexane except that it contains alternating doubles bonds (three in total)
what is weird in the double bonds of a benzene ring
Normally, double bonds are shorter than single bonds. However, experimental analysis shows that the bond length between all carbon atoms is the same, and that it is intermediate between what is expected for a single bond and a double bond. This leads to the idea that the double bonds shift positions. Benzene is said to have a resonating structure (The bonds are constantly shifting position, this process is called resonance
how can you represent benzene rings’ resonating bonds
Often the resonating bonds are indicated as a circle. In fact, it is customary to leave out the C’s and H’s altogether
what are compounds involving benzenes called, why
Compounds involving benzene are called aromatic compounds because most have strong odours. There are two types of aromatics: those in which benzene is attached to a carbon chain and those in which other groups are attached to a benzene ring.
what is a phenyl group
When benzene is attached to a carbon chain it loses one hydrogen and is called a phenyl group (-C6H5)
what are aromatic hydrocarbons used for
Aromatic hydrocarbons are used as fuels, solvents, dyes, drugs, pesticides, and herbicides
what are some famous benzene rings
Perhaps the most widely used example is aspirin, otherwise known as acetylsalicylic acid (ASA
Another example is the explosive, TNT, or trinitrotoluene. Its IUPAC name is 2-methyl-1, 3, 5-trinitrobenzene. Methylbenzene is also called toluene, thus the name trinitrotoluene with the acronym TNT
what are unsaturated hydrocarbons
If insufficient numbers of atoms are available to give each carbon a bond to four atoms then we say that the hydrocarbon isunsaturatedand the molecule will have somedoubleortriplebonds
give a quick overview of alkenes
the alkenes (general formula, CnH2n) contain two less hydrogen atoms than the alkanes with the same number of carbon atoms. Since each carbon must have four covalent bonds, the lower H-to-C ratio necessitates that a double bond be placed between one pair of carbon atoms. Because of the presence of a double bond, the term unsaturated is applied to the compounds in this series. Each carbon atom that is part of the double bond in an alkene is bonded to two other atoms (in a trigonal planar arrangement)
give a quick overview of alkynes
Alkynes are hydrocarbons that contain a triple bond between one pair of carbon atoms. The alkynes contain two less hydrogens than the corresponding alkene (or four less than the corresponding alkane); hence the general formula for alkynes is CnH2n-2. The alkynes, like the alkenes, are called unsaturated because they contain at least one multiple bond.
Each carbon atom that is part of the triple bond in an alkyne is bonded to one other atom
