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Unformatted text preview: Alkynes 1 Copyright, Arizona State University Copyright, Arizona State University Alkynes Developing Synthetic Methods (more...) 1 Nomenclature (more...) • Priority: alkenes = alkynes > halides, i.e number the chain to give either the alkene OR the alkyne the lowest number, whichever wins, if there is a tie, give the alkene the lowest number. • Suffix: -yne, if the structure contains BOTH and alkene and an alkyne, put the -ene before the -yne • IUPAC has TWO methods for naming alkynes (and alkenes). One puts number specifying the position of the triple bond at the beginning of the word, the second puts the number before the "-yne" (better way for complex structures that contain both alkyne and alkene functionalities, below). You can use either. Examples Br 2-bromohept-(2Z)-en-5-yne 1 2 3 4 5 6 7 note - dropped "e" 2-pentyne 1 2 3 4 5 pent-2-yne or • as names become more complicated, a better strategy is to put the number immediately in front of the functional group that it refers to, in the example above on the right, the 2 clearly refers to the position of the double bond and the 5 clearly refers to the position of the triple bond • when there is a "tie' (and only when there is a tie), the alkene takes priority 1-phenylethyne CH C C H 2 C CH 3 H CH (3S)-methylpent-1-en-4-yne Some common alkynes and common (non-IUPAC) names CH CH C CH 3 CH CH 2 CH 3 C CH CH 3 C C CH 3 acetylene 1-propyne 1-butyne 2-butyne CH C Ph phenylacetylene Ph C C Ph diphenylacetylene 2 Structure and Properties (more...) Internal Alkyne Terminal Alkyne C C R R` C C R H sp • sp hybridized carbons give alkynes distinct properties note order H 3 C CH 3 H 2 C CH 2 HC CH Hybridization C-C BDE (kcal/mol) C-H BDE (kcal/mol) C-H Length (Å) sp 3 sp 2 sp ~90 ~174 ~231 ~101 ~110 ~117 1.10 1.08 1.00 Ionization Potential 12.84 10.58 11.44 π electrons C-C Length (Å) 1.53 1.33 1.20 lower energy higher energy • sp carbons have stronger and shorter bonds, BOTH C-H and C-C • ALL of the electrons, in both the sigma- and the pi-bonds, are held closer to the nuclei in smaller orbitals, sometimes the sp carbon is described as being more "electronegative" than an sp3 hybridized carbon • LOWER energy pi-electrons in an alkyne compared to an alkene (alkyne has larger I.P.) Alkynes 2 Copyright, Arizona State University Copyright, Arizona State University Alkynes PROBLEMS Alkyne Nomenclature In each case, give the IUPAC name for the provided structure (ignore stereochemistry unless specified) 1 (easier) CH C CH 3 CH 2 CH 2 CH 2 CH 3 C CH 3 Answer Correct Y / N 2 (easier) CH 2 C CH CH 2 CH 2 CH CH 2 Answer Correct Y / N 3 (standard) Br Answer Correct Y / N 4 (standard) Answer Correct Y / N 5 (standard) Answer Correct Y / N 6 (standard) C CH CH 3 C C CH 2 CH 3 CH 2 CH 3 Br CH 2 H 3 C Answer Correct Y / N 7 (standard) H 3 CCH 2 CH 2 C CCHCHCH 3 Cl Br Answer Correct Y / N 8 (standard) Answer Correct Y / N 9 (standard) CH 2 CH 2 CH 2 C CCHCHCH 3 Cl Br Br Answer Correct Y / N 10 (standard)...
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- Spring '12
- Alkyne, Acetylene