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Unless chemistry has changed significantly since I majored in it in the sixties, a methyl group is CH3. If the forth bonding site is a hydrogen, you have methane, CH4. If it is a hydroxyl group (-OH), you have methanol, CH3OH, commonly known as methyl alcohol or wood alcohol. Replacing a hydrogen with a second -CH3 to methane gives you ethane, CH3-CH3, If a hydroxyl group is substituted, you have ethanol, CH3CH2OH, commonly known as ethyl alcohol or grain alcohol. Isopropyl alcohol is an alcohol. Its formal name is 2-propanol and its chemical formula is CH3-CHOH-CH3. n-propanol is an straight chained isomer, commonly called n propyl alcohol. Its formal name is 1-propanol and its chemical formula is CH3-CH2-CH2OH. Both isomers have three carbon atoms, seven hydrogen atoms, and one hydroxyl group. Any saturated hydrocarbon which has a hydroxyl group substituted for a hydrogen is an alcohol. Pentanol is a five carbon alcohol commonly known as amyl alcohol.Methanol = 1 Carbon + 1 methyl group, it is the simplest alcohol
Ethanol = 2 carbons + 1 methyl group.
Both are extremely toxic to pretty much all living things.
isopropyl = a 3 carbon active group that is connected to a another group at the second carbon - it is not an alcohol. isopropanol is a 3 carbon chain with the methyl group attached to the middle carbon.
Note the names of the alcohols are almost the same as the familiar gases, methane, ethane, propane, etc. Same compounds with an -OH instead of an H at one of the carbons.
Rubbing alcohol is composed mostly of denatured alcohol.
Denatured alcohol is ethanol with additives that make it poisonous. Ethanol kills most micro-organisms on contact - it is extremely poisonous. We use 200 proof around the lab to sterilize dissection tools or to clean stuff that should not be bleached.
Not sure why I said methanol above when I should have said ethanol. No biggie, the point remains.
Grain alcohol is denatured to make it unpalatable and to prevent it from being purified to a palatable state by distillation. Methanol with a small amount of benzene added is a common denaturant although other formulas are used. Grain alcohol is denatured to avoid paying a heavy tax which far exceeds the cost of manufacturing the product. Denatured ethyl alcohol was sold as rubbing alcohol when I was young but it is more common to see 70% isopropyl alcohol labeled as rubbing alcohol now. Denatured ethyl alcohol is sold with paint products as methylated spirits.